Roman Aqueducts

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Hey guys, hope you're doing well.

Welcome to today's episode all about Roman Aqueducts, that marvel of ancient engineering.

I've just finished recording the interview.

I absolutely loved it.

In particular, delving into the nitty-gritty details all about how Roman aqueducts actually worked and how they were maintained.

Now, that might not be a topic for everyone, but for me, I love that nerdy stuff.

It probably reveals quite a lot about me, but hey, there you go.

I hope you guys enjoyed as much as I did just now recording it with our guest, Dr.

Duncan Keenan-Jones, professor at the University of Manchester.

Right, let's go.

Aqueducts.

A type of architecture that has come to epitomize ancient Rome.

And some of them still stand as magnificent legacies of the Roman Empire today.

Like the massive aqueduct bridge, the Pont du Gard, that spans the river Gardon in France.

So what do we know about the Romans and their aqueducts?

How did they build them?

How widespread were they?

And just how central were they to Rome's success as a city and as an empire?

This is your guide to Roman aqueducts with our guest, Dr.

Duncan Keenan-Jones.

Duncan, it is such a pleasure to have you on the podcast today.

It's great to be here.

Thanks for the opportunity.

You're more than welcome.

Now, last year we explored Roman roads and it feels like Roman aqueducts is another key piece of architecture that we associate with the Romans today.

It is so iconic of the ancient Roman civilization.

Exactly right.

And actually the Roman censor who built the first Roman road also built the first Roman aqueduct, Appius Claudius.

So they're really closely linked like that.

When exploring the story of Roman aqueducts, I mean, what types of sources do we have?

Is it a mixture of literature and archaeology combined?

Yeah, so in terms of the high literature, they don't often make a big mention of the Roman aqueducts, but we do have a manual, I guess, to the water system of Rome left by one of the water commissioners around AD 100, a guy called Sextus Julius Frontinus.

So we've got that.

We've got quite a lot of inscriptions as well that the emperors left showing what a great job they were doing providing water for the people of Rome.

And we also obviously have archaeological remains.

At latest count, there's more than 2,700 ancient aqueducts around the Mediterranean area and in the area of the former Roman Empire.

So 2,700?

Yeah, and they're still finding them and adding to that count.

It's extraordinary.

And I love the fact that they can still discover aqueducts today because I guess your mind immediately you picture the big grand ones, the Pont du Garde or the ones in Spain or Italy today, but I'm guessing they come in all shapes and sizes.

Yeah, and most of them, most of the distance of the aqueduct, the route was actually underground rather than, it was only where they had to cross a depression or something like that that they went to all the effort of building that big bridge.

And actually, the very earliest ones were almost entirely underground.

And we think that's for security reasons.

They were worried that when the city was besieged or something, that people would be able to find their water supply supply if it was above ground.

And we've all can picture a Roman aqueduct in our head, but how do they work?

How do Roman aqueducts work?

Yeah, well our word aqueduct comes from the Latin aquae ductus, which just means leading of water.

And so that's what the Romans did.

They built a channel to lead the water from an elevated source, a spring or a river, all the way downhill under the power of gravity to a town or an agricultural area, generally a town.

So while they had a few ways to sort of negotiate the terrain, they could drive tunnels through mountains or they could build these bridges across depressions, most of the time they're just below ground level, hugging the terrain, leading that water downhill.

And is it a constant, the fact that, as you mentioned, kind of making the most of gravity, the fact that these aqueducts, will they always have a very gentle downward gradient from source to final place the end of the aqueduct yeah they seem to have aimed for about 40 centimeters per kilometer, as far as we can see.

That's a pretty common gradient.

So yeah, not a lot.

And that was actually a difference that the Romans made.

They drew upon earlier Greek aqueducts and other civilizations around the Mediterranean, but these really shallow gradients were a real hallmark of the Roman system.

Their skill in surveying allowed them to do that.

The idea behind Roman aqueducts, is it simply the practical purpose of bringing water from a reservoir, from a water source, to a centre of settlement?

I guess whether it's a city or maybe something a bit smaller.

That practical purpose is always there, always important.

But from the very beginning, it's also about show and prestige, I guess, at the same time.

So Appius Claudius is, as I said, known for building the first Roman road, the Via Appia, but also wanted to be remembered for building this aqueduct.

So I gave his name to both the road and the aqueduct, the Aqua Appia.

And his colleague, so all Roman magistrates were in pairs generally, so that they would share the power and no one person could get the priority.

And his colleague was so disgusted with his grandstanding and also with his, I guess, with some of the things he'd done, throwing people out of the Senate for various reasons, that he actually quit in disgust.

and left Appius on his own to finish the Aqua Appia.

So it was also about prestige and power at the same time.

And as aqueducts, you know, they're building, it strews both the Roman Republic period and the imperial period with the emperors and, you know, these very, very important, powerful figures.

Consistently throughout those centuries, can you therefore also see when someone builds a new aqueduct?

Yes, in many cases, it has that practical purpose, as you've highlighted, about bringing water to places, but also It's a statement of power.

It's showing off the might of Rome, the engineering, the architectural achievements of the Roman Empire.

Exactly.

And

those bridges in particular, like the Pundu Garde that you mentioned, visible signs in the landscape.

Everyone passing in that area knows that there's a new regime in town who can control the very landscape, the very water and environment of the area.

So it also has that sort of warning, I guess, to to people that the Romans are in control.

But it's also something that people like to have.

Many people in areas that were conquered by the Roman Empire wanted to have running water in their properties.

They wanted to have baths.

And so it was also something that some individuals in those areas took on themselves too.

So how central do aqueducts become to the growth of cities all across the Roman Empire?

Is it a critical central piece of infrastructure?

that people all across the empire were demanding, were really wanting?

Well, it's definitely a key part part of Roman urban living.

As we've seen, there are so many, and so essentially every town worth the name that thinks of itself in some sense as Roman wants to have its own aqueduct.

To go back to Frontinus, Rome's water commissioner, at the outset of his handbook, he compares the aqueducts of Rome to the indolent pyramids and the renowned yet useless works of the Greeks.

So for Frontinus, he saw it as something quintessentially Roman, practical, but in that way, showing how the Romans were different from their predecessors.

It's almost like the seven wonders of the ancient world, isn't it?

All of them, apart from the lighthouse, one of the things that sometimes we forget is that they don't have a practical purpose at all.

They're just to awe and to show off.

But with the aqueducts, as you say, they have that added purpose, is that they are bringing running water to hundreds, if not thousands of people in places all across the empire.

Yeah, definitely.

I mean, Rome at the time that it eventually had 11 aqueducts in the ancient period, and it probably had a million people by that stage.

And you couldn't have had a city like that without the aqueducts.

You just couldn't get enough water in one space to get that many people together.

And so that's really one of the reasons that Rome was the largest city the Mediterranean had yet seen.

You've done a lot of work around the archaeology of aqueducts in Rome in particular, and we're going to really explore that as our chat goes on.

I would like, though, to also ask about endpoints for aqueducts.

So we have in our mind this idea that they did supply cities and centres of settlement.

But were there other places where people were living in the Roman Empire that aqueducts sometimes went to alongside those big centres of urbanism?

Yeah, so we do see some aqueducts being used for irrigation.

And we have, in fact, some of the inscriptions that tell us how they were organised.

different pots were allowed water at different times, that they would share it in that way,

and that you would close your sluice gate, and then it was your neighbour's turn to open theirs.

And this seems also to have been a system sometimes used in some of the cities as well.

And in fact, up until the 1960s, in places, parts of Sicily, there was essentially a Roman-style water distribution system in many of the towns there.

And we have some of the minute books left from these time-based and other distribution systems in neighborhoods.

And if you were really rich, if you owned a villa, let's say nearby Vesuvius or somewhere really fancy in the Roman Empire, if you had enough money, could you get your own aqueduct as well so that you have your own source of water for your rich villa in the countryside?

Yeah, you definitely could.

And we have letters from, for example, Cicero, the great Roman lawyer and orator, politician.

who is doing some work for his brother, who's away managing a different part of the Roman Empire.

He's gone to one of his villas that his brother owns, and he's spoken to the subcontractor who's putting in the Roman aqueduct to supply the villa with water.

And he said, yeah, this guy's basically, he knows what he's doing.

He seems honest enough, and he thinks it can be done for this much at a certain gradient.

It'll be about two kilometers long, for example.

And so this is something that elite Romans definitely wanted as part of their...

their country estates too.

And in what types of structures did aqueducts end up in?

Let's say if they end up in a city, should we be imagining big public fountains or kind of the equivalent of water fountains, drinking fountains or something else?

What should we be thinking about?

Well, when they reached the city, generally the aqueduct was brought to the highest point of the city so that you could use gravity to distribute the water around the city.

And it would go into, from there, there would be a basin.

or a large tank and lead pipes would generally run from there to supply different parts of the city.

And so they would supply a number of street-side fountains.

For example, within the town of Pompeii, the best evidence we have for a Roman water system,

there's a fountain within roughly 50 meters of any particular dwelling.

So you only had to go 50 meters to collect your water for the day.

But if you were...

in the wealthiest 10%

of the property owners in Pompeii, you would actually have the lead pipes running straight into your house.

They would be connected.

You would have a fountain in your courtyard, your entrance courtyard, where all your colleagues and your clients would come.

That would impress them.

And you would have even perhaps a small bath suite with a few rooms in your own house.

Of course, there would be large public baths too, like the baths of Caracalla at Rome, and also monumental fountains that sort of displayed...

the munificence and the wealth of the emperor in other ways, especially in the capital, Rome itself.

Dan, can I just ask all of those questions to start off with, once again, just to emphasise the complexity of these constructions, of the engineering alongside them?

It is not just as, as we kind of highlighted already, it's not one type of aqueduct fits all.

They're so complicated in how they're designed by the Romans that that in itself, I'm sure you with an engineering background as well, is something to marvel at and be really impressed at.

Yeah, and it clearly shows us as well that they're prepared to put a lot of resources, manpower, material resources, construction materials

into building these.

So it's something that's clearly very important to them and they require maintenance over time as well and they were happy to keep putting that money into the maintenance because they saw this as a really important part of their culture.

One other question before we delve into the whole thing of building an aqueduct and we'll go through various different parts of the construction phases.

In regards to the origins of aqueducts, Duncan, do we have any idea whether aqueducts, this type of water transportation, was used in the ancient world before the Romans?

Yeah, there's quite a few famous examples.

And like so many technologies, it seems to come from the larger empires, earlier empires further to the east.

So places like the Assyrians in Mesopotamia.

There's a really famous inscription that survives in Jerusalem.

It's actually now in...

in the Archaeological Museum in Istanbul, but was found in Jerusalem.

And it describes King Hezekiah from the Hebrew scriptures, the Old Testament, who led in a channel or a tunnel really of water inside his city to help him withstand a siege by the Assyrians.

Actually, and there's this great inscription found that describes how the two groups were going from opposite ends tunneling.

And they were trying to find each other.

And you can see in the remains of the channel today, if you go in there, that they're moving around going side to side.

And eventually it says that one of the workmen heard the sound of the other group picking away.

And so then they knew where to go.

And then they went straight and completed the tunnel that way.

So that was in the ninth century BCE.

And we also find examples in the Greek world, some quite sophisticated ones there.

And it was particularly through influences with the Greek world that the Romans started to develop this technology.

In particular, a kingdom called Pergamon.

in modern-day Turkey that was one of the kingdoms that came after Alexander the Great conquered the whole of the eastern Mediterranean.

The Atelid kingdom with their splendorous theatre and library and everything like that.

I didn't really realize there was a distinct link to Pergamon there.

It's so, so interesting.

And I also love the fact you mentioned Mesopotamia because you might also think of the hanging gardens of Babylon or the great paradises and gardens of the Assyrians as well.

So you can see how the bringing of water, you know, there surely must have been an influence going back hundreds of years before the time we associate with Rome.

Yeah, indeed.

And it's a way that many different groups have shown that they're in control of the environment, the physical environment.

Yeah.

So if we go now onto building an aqueduct, I mean, Duncan, you mentioned earlier lead, and we will explore that as time goes on.

But what are the other main materials that the Romans used to build aqueducts all across their empire?

The earliest aqueducts were largely built out of stone, large pieces of stone, ashlar masonry laid in courses.

But Pretty quickly, the Romans developed concrete by burning lime and adding chunks of stone to it.

And this provided a quicker way, an easier way in many ways, because when you poured the concrete, it would match the shape of the formwork that you had put there.

And so this became used to build the aqueducts, except in certain areas where the aqueduct was particularly on show, say where in the countryside just near Rome or where it was crossing a road, they would often go back to the ashlar masonry because it looked so much better.

But so they used that concrete as well.

They used brick often as a facing or a formwork for the concrete.

And then for the pipes they used a number of different materials.

So lead was easy.

It's got a very low melting point.

You can melt it in a very simple fire, pour it into a mold and roll it up to make a pipe in that way.

But they would also use ceramic pipes.

That was something that they got from their Greek predecessors who tended to make their aqueducts out of pipes of ceramic turned on the wheel and then fit together.

They would tunnel out from wooden logs sometimes to make wooden pipes that were joined with metal collars.

And sometimes they would also make a stone pipeline, particularly where they would be doing a sort of reverse inverse siphon rather, where the water would be led down one hill under pressure.

It would go across the ground and then would go up the other side of the depression actually.

Obviously not as high as it started.

It can never go above that height.

But the pressures could get quite high at the bottom of a big inverse siphon and so they would sometimes build these stone or lead pipelines to withstand that pressure too and you see time and time again today in games and films and so on the idea of the the aqueduct being really high up you've got the water channel on top and then it's open on top it hasn't got a roof or any cover to the water channel now how accurate do you think that is or would the romans have realized that they don't want anything potentially infecting the water.

Maybe that's thinking too much.

I mean, do we think it would have had a cover or something like that?

No, definitely they did.

And in fact, in almost all examples that we've found, they did have a cover.

And in fact, some of the writers, the architect Vitruvius, for example, or the encyclopediast Pliny the Elder, described that because there's a cover on the top, you need to have a manhole, an access shaft,

every certain distance, at a regular distance, anyway, often about 32 meters or so, so that you can get inside, do maintenance, fix up any problems and these covers frontinus tells us had a metal cover to prevent things from getting in there and we've actually found one of these just upstream from pompeii the only one we've found that survives that's in situ and i guess one other thing just because we did a documentary at petra not too long ago and we focused on the incredible water system there and something someone pointed out one of our guys pointed out was the fact as if you as you were walking into petra and you had the water channels either side, something that you might forget today is that you could also hear the trickling of water too.

Should we also be imagining that, that people walking through the streets of Pompeii, Rome, or maybe Roman London or elsewhere, you would hear that trickling of water from the nearby aqueduct as you went through the streets?

Well, definitely, and especially from the piped distribution system inside the city, because we know that all the fountains in Pompeii are essentially orientated with an overflow groove cut into them so that the water would overflow out into the street and actually played a vital role there in keeping the streets clean.

We think that there's a lot of animals being used for transport.

There's a lot of animal dung in the streets as a result.

And these aqueducts are helping to flush the streets clean into the sewers.

To the point that Frontinus describes that it was actually illegal to divert that overflow from the fountains for another purpose unless you had paid to do so.

So that trickling is going to be heard as well.

Also from the water towers that were placed throughout the system.

These were large towers above ground level, often up to the second story of the buildings.

And the lead pipes would lead the water up on top of these towers.

It would sort of be reset to atmospheric pressure in an open basin on the top.

But if there was a fluctuation in the system, a pressure fluctuation, the water might eject out the top of that basin and run down the sides of the water towers.

And we can see that evidenced by the limestone deposits from that water at Pompeii that have formed on the outside of those towers and are still there today.

So yeah, that sound would have been all throughout the city.

It's extraordinary and great to picture in your mind

the sounds alongside the visual idea of these Roman aqueducts.

I must ask one other thing to do with the architecture of aqueducts, Duncan, is that a thing we get in our minds time and time again is that they're up high and almost the architectural style is just arch after arch after arch, these arcades.

I mean, why do the Romans build aqueducts with that very distinctive arch style?

Yeah, well, there were a few arches around the Mediterranean before the Romans, but the Romans are the first civilization to really make widespread use of the arch.

And so

it's easier because you're using less building material than building a sort of causeway or something that might be very very high.

And it also gives access from one side to the other.

If you think of the city of Rome, the aqueducts that were approaching it, they wanted to be kept as high as possible so that the water could supply the highest points on the famous hills of Rome.

And so they're running in an arcade, the latest ones are running in an arcade nine kilometers long.

outside the city to cover a depression up to the city itself.

And that arcade gets up to 32 meters high.

So it would be a real impediment to the landscape.

You would have to go a long way around if you wanted to pass that.

But because you've got the arches there, you can pass under easily as well.

And in fact, several of the key roads leading into Rome pass under these archways of the aqueducts.

And that's where the emperors located their inscriptions above those arches where they get the most traffic and they would get the most visibility for their commemoration of what they've carried out.

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And if we now talk about some very complex cases of aqueducts, because this leads into, I know one that you've done a lot of work around, and we will get to Rome in time because that's another extraordinary story that I know you've done a lot of work on.

But do we therefore get a sense when you explore the various aqueducts that have survived, you look at the architecture that has survived, and I guess you also look at the varying length of some of these aqueducts too and the natural features they had to overcome.

Do you very much get a sense that there are a certain few aqueducts that are very clearly much more complex than any others?

Yeah, and that's often because of the environment in which they were made, because of the physical topography, or it can be for more cultural, social reasons.

So one example is the aqueduct that supplied Nîmes with the famous bridge the Pont du Gard as part of it and it gives us an insight into how these aqueducts were designed and planned because the first step was to find a source of water that was sufficiently large of good enough quality that it could be led to the city and so it had to be high enough.

had to be higher than the city itself and you wanted to have a fair bit of fall to play with to make it easier, to make the planning easier.

But at Nien, the closest and the best source that they could find was at a place called Uze,

which was about 20 kilometers away as the crow flies, but only 17 meters above the town.

And so.

That's a problem.

Yeah, quite tricky.

And so it probably would have been difficult to know if it was higher than the town before they started surveying it.

And they probably had to walk potential routes many times with their surveying equipment before they settled upon a route.

But it had to go across this enormous valley where the Gardon River runs through.

And they were gonna have to build the biggest aqueduct bridge that had ever been built in the Roman world and that was ever built in order to get across there.

And so they tried, because they were a bit worried about whether it would fail, they tried to make it as low as possible, the bridge.

And so this meant that the aqueduct was quite steep in the first bit up to the bridge, but once it got across the bridge, there wasn't much fall left to use to get the water to the town under the force of gravity.

So the gradient after the bridge is only seven centimeters per kilometre.

And so it required a lot of surveying skill to make sure the water kept moving downhill, that it didn't just stop.

It also made the flow rate less, so they got less water as a result.

So while they managed to overcome the obstacles of the topography around them, they had to make some sacrifices at the same time.

You mentioned the Pont de Garde there, and we will put a link to the Pont de Garde images of the Pont de Garde in the description of this episode because it is such a striking surviving example.

You also picked on something there, Duncan, if we go on a quick tangent, something that I completely overlooked was looking at the building of the aqueduct themselves, the materials involved, but also the planning beforehand.

As you said, people going out there with their equipment to level the lands to get an understanding of, you know, how high up the reservoir was, going back and forth, back and forth.

Do we know much about that whole surveying of the landscape beforehand to plan out constructing a big aqueduct?

Yeah, we do know a little.

We have a few technical treatises left by a technologist called Hero of Alexandria, who worked in the first century CE.

He leaves a treatise on surveying and we've also got some of the writings of the Roman surveyors who laid out plots of land that were given to veteran soldiers after they were demobbed from the Roman military.

And so we have some information but not as much about the actual planning of aqueducts as we would like.

But we know some of the technology that they used.

They had essentially a sort of big wooden trough that was a bit like a water level that they could sight things down and they also had a big long metal pole that was simply supported in the middle and that would kind of balance and they could sight down that as well as well as some other things that they could ratchet up and down to different angles to to also

survey the distance but it's thought that they surveyed the the floor of the channel quite roughly and kind of pegged it out over a long distance I mean they must have first come up with some sort of broad draft routes, we might say, and then further

further specified the route as they as they got down to the nitty-gritty.

They came up with this sort of this pegged out route, but then they would start building and they would keep surveying the floor as they were building to make sure that it was still working.

And they might even flood particular parts with water just to check that it was actually going to work before they sort of closed over the roof and finished it off.

So they want to be absolutely sure because of the amount of effort going into it.

You don't want to end up being a little out in your mathematical in your equations and how much water you can get down because I I guess then you've got a lot to answer for.

Yeah and it's particularly difficult where the ground doesn't stay still either.

So around the volcano of Soma Vesuvius right near Pompeii we can see that before the eruption and

the volcano was swelling as the magma and water moved underneath the volcano and that after all the eruption materials came out that it kind of collapsed again and there was one of these one of the most complex Roman aqueducts, in fact, the Aqua Augusta, was running, skirting around the edge of the volcano.

And so these changes in ground level played havoc with the operation of the aqueduct, as the part closest to the volcano became quite high and you probably had ponding in the aqueduct happening up to it.

And we found that they actually destroyed the roof of the aqueduct, perhaps so they could re-survey it after the eruption and check what repairs and changes they needed needed to make.

Can you tell us, you read my next question, which was going to be about the Aqua Augusta, because this seems to be a really, really interesting case study.

So what else do we know about this aqueduct that went right around Mount Vesuvius?

And from what it sounds like, with what you're saying, Duncan, unlike places like Herculaneum and Pompeii, the Aqua Augusta, I mean, it does endure past the eruption of 79.

Yeah, that's exactly true.

Yeah, so it's built, as the name suggests, by the Emperor Augustus.

He gave his name to the aqueduct, but it seems he promised it much earlier than he got that title.

That was bestowed on him by the Senate in 27 BCE.

In fact, when he's fighting for control of the central Mediterranean with another Roman called Sextus Pompey, as we know, Augustus is the adopted son of Julius Caesar.

Sextus Pompey is the son of Caesar's great rival, Pompey the Great.

And so these two second generation Roman warlords are fighting for control.

And

Augustus had to build a whole new artificial harbour on the Bay of Naples in order to train his fleet to go out and fight Pompey because he didn't have a good fleet at the time.

Pompey had much greater maritime power and he was worried his fleet would never get to practice.

They would just be destroyed by Pompey's navy.

So he made this safe harbor where they trained and eventually went out and beat not only Pompey, but also then Antony and Cleopatra at the Battle of Actium.

But he needed also some water supply for this harbour because it was in a very dry area, or not so much drier, but an area where the springs, because of the volcanism in the area, they were hot springs, very sulfurous with lots of minerals, not great for drinking.

So he needed water supply.

So he built this enormous aqueduct that had to come from 100 kilometers away.

And so he saw an opportunity on the way to also supply the other key towns in the area, to bring them on side so they wouldn't take Pompey's side in this in this battle.

So he promised them also water supply.

And when the aqueduct was actually built, it therefore supplied eight or nine towns.

We're not really sure.

Whereas every other aqueduct we know supplied one or at least, or at the most, rather, two.

And so this is a regional water network rather than just an aqueduct supplying one town.

And it's unparalleled amongst Roman aqueducts.

uh and does it endure for centuries after that so it starts with augustus you know some almost two well just just over two thousand years ago and does it endure for centuries after this incredibly complex aqueduct around the bay of naples area it does and it's quite fortunate with the eruption of 79 because of the wind direction at the time the wind was blowing from the northwest and so it didn't blow most of the ash across the main line of the Augusta, which skirted the volcano to the north.

And so it did get some ash fall on it, and that had to be excavated and it needed to be repaired because of this ground level movement that I mentioned.

And we've actually seen the results of that damage in cores that myself and collaborators have taken from the harbor of ancient Naples.

where the lead pollution from the pipes in Naples supplied by the Augusta, that disappears for a short amount of time after the eruption while they're repairing the system, getting it back online, and then starts up again.

So we can see some of the problems that they had from the eruption, but yes, they were able to repair it and it kept operating for several hundred years.

In fact, probably until the next major eruption of Vesuvius.

That was in 472 AD.

And this time the wind's blowing from the southwest, blowing the ash right across the main line of the Augusta.

And also the Bay of Naples is in a much more difficult position now.

There's been barbarian invasions, there's been plagues.

It's not the same prosperous area that can call upon Rome for support anymore.

So that seems to be the end of the aqueduct.

It's not repaired after that.

All right, 472.

Yeah, four years before the last emperor in the West is deposed.

So very interesting indeed.

We've talked about bridges in passing as well when highlighting the complexities of building aqueducts over long distances and natural terrain features like gullies and ravines, valleys.

But what about with mountains and high places?

Because I think with Italy, obviously you've got down the spine of Italy, you've got the Apennine Mountains, a very mountainous area.

Did the Romans have to try and navigate that with tunnels as well?

Do we know how they...

navigated that when building their aqueducts.

Yeah, and the Romans actually, well, as far as we can tell from their writings, elite Romans seem to have preferred rainwater to spring water.

If they were going to drink spring water, they wanted it to be from the coolest, purest mountain stream they could find, or spring, even

better.

And so they did draw a lot of their water from those Apennines, and this did lead to technical difficulties.

In the case of the Aqua Augusta, they had to take the best springs that they could find that weren't already in use.

They were in a completely different basin, a completely different watershed.

So the water from those springs would normally flow down a river and go out into the Mediterranean Sea in quite a different location from the Bay of Naples.

So they diverted that water through a six kilometer long tunnel that they had to drive through the Apennine Mountains in order to get it down into the Bay of Naples.

So this is one of the longest Roman tunnels we've found in aqueducts.

You can still see it today, can you?

So you can't, but we can tell from the remains of the aqueduct that it must have been there.

The last remains that we can find stop before this large mountain range, and then we pick them up on the other side.

But these aqueducts and this aqueduct in particular, in the 19th century, Italians were trying to bring them back into use to supply Italian towns at that time.

And so there was an engineer there called Felice Albate,

and he was looking to use this aqueduct and use these springs to supply Naples again and so he's left us with a great account of the remains so even where things have disappeared or we can't find them now we can go back to his account and see where they were at least in the 19th century.

Well there you go is that the legacy of Roman aqueducts right there on Italy.

I'd also like to go back to the number, the quantity of aqueducts in the Roman Empire.

You mentioned so far some 2,700 have been discovered.

Should we be imagining then the greatest quantity of them being in more the heartland, the richer areas of the Roman Empire?

Or can we be imagining them stretching from, let's say, Hadrian's Wall, near where you are today in the north of England, all the way down to, let's say, the Levant or a place like Petra that I mentioned earlier?

They're definitely found all over the empire.

In every corner of the empire, there are several on Hadrian's Wall.

Interestingly, some of those come from the north of Hadrian's Wall.

Wow.

So we shouldn't imagine, part of the evidence that suggests is that Hadrian's Wall is not an impenetrable barrier trying to keep out the Picts to the north, but it's a porous barrier where the Romans can control who goes north and south along that barrier.

And they're obviously not afraid to put their water source north of that wall.

And we do find them especially in some of the driest parts of the Roman Empire as well, such as North Africa.

There's an enormous aqueduct 82 kilometers long supplying the town of Carthage, Rome's great enemy that it eventually destroyed and then resettled.

And there's also aqueducts in Syria, one of the longest in fact, at around 130 kilometers long, I think, is the Kanat Firaon in Syria.

And we know a little more about those in sort of northwest Europe.

Partly because there's been a lot more archaeological work done there.

And so we've turned up a lot more.

But I would suspect there's many more waiting to be found in some of those less studied areas such as mesopotamia or or syria or north africa keep an eye out for new aqueduct discoveries archaeological discoveries in the future but of all the cities these urban centers in the roman empire duncan none of them had as complex a water system series of aqueducts and pipes leading off water basins and so on than rome itself am i correct correct?

I mean, can you tell us about this?

Because this is extraordinary.

Yeah, so Fontinus tells us that before the aqueducts, people would collect rainwater, would take water from the river Tiber.

That's really pretty much the only mention of people drinking the water of the river Tiber, which might tell you something about how

the quality of the water at the time.

But in 313 BCE, as we've mentioned, Appius Claudius builds this first aqueduct.

And then after that time we have several more built by victorious Roman generals who are bringing back a lot of loot that they've taken from their enemies because it costs a lot of money to build one of these aqueducts and so it's often once they get this kind of windfall that they they look to do this and it's a good way of of leaving your legacy on the city of rome itself so we have we have one built in 272, another built in 144 BCE.

And then we have the period of the Roman civil wars, essentially, where the aqueduct system is neglected.

And we know this partly because, again, of the samples we've taken from Ostia, the mouth of the river Tiber, where we can trace, again, this lead pollution from the water distribution system in Rome.

We see the amount of lead pollution increasing over time.

until we get to these civil wars and then it takes a big nosedive.

The people in charge of Rome had other things to worry about than keeping the aqueducts working properly.

But then Augustus puts an end to that as we've seen.

He sees off Sextus Pompey.

He sees off Mark Antony and Cleopatra and he can come back to Rome and his argument for remaining in control of the Roman Empire is one that he's only the first citizen, he's not a king or an emperor, but two, that he's managing it in a really good way, in a peaceful way, but also in an organized way.

And he shows that partly through his reorganization of the water system at Rome.

He doesn't do it all himself.

He lets his friend Agrippa build a lot of it.

And so that suggests that he's not a king or an emperor.

He's just one of many.

But they build together three new aqueducts to supply the city.

So they double the number.

Almost, there's actually four before Augustus.

But they also repair the existing aqueducts and put in a lot more fountains, a lot more lead pipes and baths as well.

So we get some of the first really large bath complexes.

And so we see this in the lead pollution at Ostia in our core, that it increases greatly in this time, at Augustus' time.

Before we go on from that, Duncan, just kind of bringing back to the earlier ones that you mentioned from the Republican period, the Roman Republic, as you say, with those kind of victorious generals, I was just really struck by the dates you mentioned.

So 272 BC, that's when the Romans have just defeated Pyrrhus.

Exactly.

The warlord, Pyrrhus, Hellenistic warlord Pyrrhus in South Italy.

So they basically become the top dogs in Italy.

144, so that's just after defeating Carthage and Corinth.

So another big victory as well.

Then like civil wars, Sulla, Marius, Caesar, Pompey and the like.

And

it's just interesting, it's reaffirming your point, isn't it?

Key moments when Rome is really extending its control early on is the purpose behind building those early aqueducts before Augustus emerges onto onto the scene.

Yes, exactly.

And it's one of the many ways also to keep the city of Rome on side.

As we know,

in the Republic, there's many different powerful families and individuals all sort of seeking dominance or seeking priority.

And so by leaving an aqueduct, you leave your family name on it.

Your successors

can...

can draw upon that.

And we see that in the coins minted by some of the successors.

They refer to these aqueducts, like the the Aquamarchia, showing that they're part of a family that has done great things for Rome.

And like providing grain, like eventually providing entertainment in the form of the Theatre of Pompey, providing running water and bathing is another way to keep the people on side in Rome and prevent political instability there as well.

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Do you think it's surprising at all that Julius Caesar didn't leave us an aqueduct in Rome?

Well, he certainly had big plans.

So

not so much in the provision of water, but in the management of the Tiber River, for example.

He left us with plans that Cicero records in a letter saying that he was actually going to divert the Tiber around the Vatican Hill on the other side so that floods wouldn't hurt the city so much.

And so he definitely had a lot of big plans.

Maybe there were plans for aqueducts as well.

But as we know, he only had about four or five years as dictator in Rome before he's assassinated.

And so many of these plans never came to fruition.

And it's left to his adopted son and great-nephew.

Augustus,

as a dutiful Roman son, to complete the things that his father had started.

Duncan, thank you for allowing me that tangent right there.

So let's continue the story from where he left off.

So there's six aqueducts in Rome by the time of Augustus.

What happens after that?

Yeah, actually seven.

I left out one there, the Aqua Tepula.

Actually, one of the ones that's probably not regarded highly by Frontinus.

So there's seven by that stage.

Tiberius.

and Gaius or Caligula don't do too much.

They're Augustus's successes in terms of building new aqueducts.

They keep maintaining the system augustus has actually left a group of enslaved people to work on the aqueducts and to maintain them so that continues but then well actually i've i've done gaius a disservice there because he starts in train the building of two new aqueducts at the same time the aqua claudia and the anio nobus but again he's only in in control for a short period of time and it's his successor Claudius who finishes those two about 10 years after they were started.

And he actually opens them on his 61st birthday.

We know that from Frontinus.

And on the fifth anniversary of him taking the role of censor, we remember that under the Republic, it was the censors who were responsible both for the moral purity of the city, but also for the physical purity and cleanliness.

And so water supply was part of their role.

And so Appius Claudius was a censor.

And so by doing on the fifth anniversary of him becoming censor,

the censors are appointed every five years, he's showing that he's doing this as an old Republican censor.

And Claudius is very much an antiquarian.

He left behind studies into the ancient Etruscan alphabet and other things.

And he likes to do things in the old way.

So we can see that he's done that in this way.

So it seems like there's almost an explosion in interest, I guess.

personal imperial interest in aqueducts from Augustus onwards and the emperors realizing in Rome that a great way, does it almost kind of bring you into the bread and circuses idea that maybe it's bread, circuses and water supply that these emperors think about when they're in control of Rome because they realize that they want to get their name associated with building another of these amazing constructions, which brings in more water to the people of Rome who are ultimately the masses beneath them?

Yeah, exactly right.

And it's amazing you should say that because one of my students in her final year dissertation this year actually investigated the bread circuses and water supplies, the three main imperial benefactions in Rome.

Augustus in so many ways lays down the blueprint of what princeps, what a Roman emperor should be like, and

water supply is one of those things.

To the extent that even after the Roman Empire has fallen, it's something that's taken up by the popes in Rome.

as a way of showing that they are the legitimate rulers in Rome.

They are still doing what the rulers of Rome have always done, which is provide water.

And then does it just continue emperor after emperor, or does it finally reach an end point where they decide, right, no more aqueducts, we're done for aqueducts in Rome?

The successor to Claudius is Nero, who we've all heard of.

And as we know, he had a somewhat checkered career, especially with the Rome senatorial elite.

And Tacitus, one of those senators, records for us that he was was infamous for swimming in the water supply in the source of one of Rome's best aqueducts, the Aqua Marchia, which came from one of these really pure mountain springs.

And so he's swimming in that spring, and this kind of gets back to the people at Rome, and they're not too happy about it.

He also diverts part of the water from

perhaps at that time

the other best quality Roman aqueduct, the Aqua Claudia, it was on a par with the Marchia.

He devotes part of it to the temple of divine Claudius.

So in that way, he's showing that he's a dutiful Roman empire or emperor, acknowledging his divine predecessor in the role.

But really the water is actually going to his golden house that he's building right next door.

And so it's giving him, for example, water power to to power a rotating dining room in his golden house that actually slowly moved around,

giving the guests a different view of the city of Rome

over time.

I love how the terrible stories of Nero also extend to be a pity.

You know, you get stories of him mismanaging, mistreating the water supply as well.

It's almost like another way that these writers figure out to kind of tarnish his reputation.

Yeah, that's exactly right.

And after

Nero is deposed, after he's killed, then we have an interregnum, a period of political instability.

And the emperor that comes out on top, the fourth of the emperors of that year of 69, is Vespasian.

He's not from one of those blue-blood aristocratic Roman families.

He's a really successful general, but he doesn't have quite the same aristocratic pedigree.

And so he's looking for ways to establish his legitimacy, to start a new dynasty.

And one of the things he does, he demolishes the golden house and returns it to the people in the form of building the Colosseum that we all know.

And he's very open about that.

And he does the same with the water that Nero had diverted to the golden house.

He says that he puts an inscription up over

where the aqueduct crosses two key roads leading into Rome.

And he says that he has restored the water to the city.

So to the people, essentially, rather than keeping it kept away for the personal use of the emperor.

And so in that way, it's part of his propaganda program to create legitimacy for himself and for his children, Titus and Domitian.

And ultimately, I've got also my notes, you get to the Aqua Alexandrina ultimately as well.

Is that the last one?

I mean, how much further in time do we have to finally get to the full set of aqueducts in Rome?

Yeah, well, Frontinus comes shortly after

Vespasian's son Domitian.

He's appointed under the next emperor as water commissioner, and he tells us about plans that the new emperor Trajan has for the water supply.

And it's Trajan who builds the second last aqueduct, the Aqua Triana.

And then the final aqueduct, as far as we can see, is the Aqua Alexandrina.

There's a bit of debate about exactly when it's built and what in particular,

which particular remains are the Aqua Alexandrina?

That's not entirely clear, an area of ongoing research.

But probably built in 226, and that's the last of the ancient aqueducts.

But they have a long life after the fall of the Roman Empire in the West, a breakup in the 5th century, as you mentioned.

I guess also 226, so that's Alexander Severus, hence Aqua Alexandrina, the emperor.

But what I found fascinating, first of all, is this idea that Romans like Frontinus, I guess guess Romans in general who used the aqueducts, they had almost a tier list of which aqueducts were better than others.

And secondly, just to completely paint a picture, before I ask about water flow itself,

do we think as more aqueducts were added to Rome, were there additional parts added?

Like did the Aqua Traiana link up with the Aqua Claudia anywhere or Aqua Marchia or to kind of make it even more complex, the water system?

Or did they kind of stay separate parts of the city?

Yeah, that's a really good question.

And they did link them up.

I mentioned before how Augustus and Agrippa repaired all the aqueducts after the civil wars.

They put two of the existing aqueducts, they put them on top of a new one that they built, the Julia, to save on materials.

No point building three massive arcades leading into the city if you could just superimpose the aqueducts on top of each other.

So they kind of draw them together in that way.

But Fontinus tells us that actually every fountain within the city and he tells us there are there are more than 591 actually at the time every single one of those can be supplied by more than one aqueduct so in case one of the aqueducts is down for repairs or something you can divert the water from another one there so there are these sort of overlapping lead pipe systems and even in some cases aqueduct channels on on arcades going throughout the city and it is quite a complex system The Aquatriana that you mentioned, it came high up onto the Juniculum Hill and ran down the side of the Juniculum Hill.

In the late city, in late Rome, it supplied their, it powered rather, I should say, mills for grinding grain into bread through water power.

And it also supplied the other side of the city on one of these inverse siphons.

And we found the massive lead pipes with Trajan's name stamped on them that carried the water across a bridge, across the river Tiver, and then up the other side.

Oh, you had aqueduct bridges as well.

That's so fascinating.

Let's talk then about water flow itself.

So you've got all of these aqueducts going through Rome and I know this is something you've done on one particular one.

I think the Anio Novus, I hope I've said that correctly.

What has your research around this actually revealed about how much water flow went into Rome and whether Rome, ancient Rome, did have more water than 19th century London?

Yeah, so this has been long been a source of interest and debate, partly because Frontinus leaves us with information about the flow of water in different parts of the aqueduct system, both in the aqueducts outside the city themselves, but then at different points inside the city in the lead pipe distribution network.

But it's problematic.

We're lucky to have Frontinus's manual.

It survives in only one copy, made in the 9th century, copying an earlier text which survives, goes back to, that chain of survival goes back to around 100 CE.

Luckily, this copy was found by a Renaissance manuscript hunter, a guy called Poggio Bracciolini, who's looking in the archives of the great monastery of Monte Cassino and manages to find this text.

one that he's heard other writers talk about, other Roman writers, but no one has a copy of.

He finds it.

But unfortunately, it's been copied many times and it's not in a great state.

People have made mistakes while they're copying it.

And so a lot of the figures that Frontinus gives are difficult to work out.

They don't always add up.

But it seems that they might not have even added up at the beginning.

Frontinus is...

He says that his manual is essentially for his successes in the role of Worm's water conditioner, so they know what to do.

And so they don't have to rely on their social inferiors working under them to tell tell them how to run Rome's water system.

And Frontanis is very concerned about fraud on the part of his underlings.

He thinks that people are paying them and they're diverting some of the water to these people because of the kickbacks that they're getting from members of Rome's elite.

And he wants to present the impression that he can account for every drop of water in the system, anywhere.

So in the aqueduct or in the distribution system.

And he wants to use this as a deterrent to both his underlings, but especially to his fellow members of Rome's elite, so that they won't dare try and steal water because Fontinus, with his calculations and his mathematical accuracy, will be able to find them out.

But it seems that he didn't have a good way of measuring the speed of the water.

All the values of the flow rate that he gives are actually values of the cross-sectional area of flow.

So

they're the size of the channel, not how much water's flowing through it.

And so it seems that he probably found it quite difficult to work out how much water was in the aqueducts, even if he could work it out to some degree in the city itself.

And so

people have tried to sort of fix these and to work out how much each of his, each unit of water flow that he has, how much it might actually be in water rather than just in area.

And

the values that they've come up with were what was being used in the 19th century in Rome, because that seemed to be the best thing to use,

because it probably had the greatest continuity with ancient Rome.

But what we've done is we've looked at where the limestone deposits that have formed in the aqueduct.

So the aqueduct is The Rome's aqueducts carry hard water.

And so like happens in your shower or in your tap, if you live in an area with hard water, you'll get a white chalky buildup in them.

And so the same thing built up on the insides of the aqueducts.

It had to be periodically removed to keep them operating.

Hence the maintenance that you mentioned earlier, got it, right?

Exactly.

And we can tell how deep the water was by those deposits, because they've been left at the end of the aqueduct's life.

And using hydraulic engineering calculations, we know the gradient, we know the size of the channel, we know how rough the walls are, and we we know how deep the water was.

We can work out how much was flowing there.

And we found that at the end of the Anio Nobus' life, that it's much less than people had thought by using the calculations of Frontinus.

It's less than half, in fact, of that amount.

And so while Rome was an amazing system, it was supplied with

an amount of water unmatched up to that point, and it allowed such a big city to actually exist.

It's not quite at the same level that people had thought in the past.

We have mentioned the words lead piping from time to time.

So the big question is, did this lead piping, as a consequence that the Romans didn't realize, was it actively poisoning the Roman population that was drinking from these water supplies?

My short answer would be in some cases, yes.

And it seems to depend on a case-by-case basis.

For quite a long time, scholars thought that it wasn't at all.

And that was because of two reasons.

One was again these limestone deposits that I mentioned.

They're building up on the inside of the pipes, people thought, and so creating a protective barrier between the water and the lead, not allowing the lead to get in there.

But from the pipes that we've studied and that many others have studied, you don't actually find these deposits so much within the pipes themselves.

And that's because of the way the pipes work compared to the channel of the aqueducts.

So in the aqueducts, the water is not flowing full.

It's maybe half full a lot of the time.

And there's a lot of interaction between air and water in the big aqueduct channel.

This allows carbon dioxide to pass out of the water.

It changes the chemical equilibrium in the water and allows these deposits to form.

But in a pipe, it's generally flowing the whole diameter of the pipe.

There's not so much water in there, and there's not so much air in the pipe.

There's less interaction between the air and the water and it doesn't have the same chemical effect.

So probably that's not helping.

The other was that unlike our current systems where we sort of leave water in a pipe until we need it, then we turn on the tap and it comes out, Rome's system was constantly flowing and taps were used.

to divert the water from one place to another, but not really to hold it in a pipe.

They didn't really have the storage to do that within the system.

And so it's not spending as long in contact with the lead pipes as it was, for example, in 19th century North America or in Europe or Britain.

So they're probably not getting as much lead out there, but we wanted to test that.

So we took some of the limestone deposits from the city of Pompeii, not from the lead pipes, but from other features such as basins or baths.

or the water towers themselves and we analyzed how much lead they had in them and we found that they had more lead than in the aqueduct leading to the town or than in other aqueducts nearby.

And so definitely some of the lead from the pipes is getting into the water once it gets into the town.

And people are drinking that and this will be causing health problems, the terrible health problems that we know from modern studies of lead poisoning, things such as infertility, miscarriage.

but even mental issues to do with impulse control and things like this leading to higher rates of antisocial behavior and so forth.

So that might have been a problem in some Roman towns, but it's probably not so much because of the water that they're drinking, but because maybe some of the medications that they're using, which contain lead that they're putting on their face, and also cooking up things such as wine in lead vessels.

because it gave them a sweeter taste.

So there are other ways that were probably worse vectors for lead ingestion for the people in the ancient Roman world.

Okay, I'll refrain then from asking, did aqueducts contribute to the fall of the Roman Empire?

Duncan, this has been absolutely fascinating.

I wish I could ask so many more questions.

I still have so many more questions, but I think we've run out of time.

The legacy of aqueducts, we could do another episode completely on and so much more about the water systems of ancient Rome.

Is there anything else you'd like to mention about aqueducts before we completely finish that we haven't covered in the chat?

I guess just their legacy down to the present day, which was that for millennia really, after the Roman period, Roman water engineering was looked upon as the apex of that science or that area of engineering up till that present time, such that as I mentioned in the Renaissance and later, they were trying to rebuild the Roman aqueducts, repair them to work again.

So

we still have several supplying parts of Rome today that were repaired in the Renaissance.

The fountains, the famous fountains in the area of Rome, such as the Trevi fountain and the fountain, the Barcaccia at the base of the Spanish steppes, they're supplied by the Aqua Virgo, built by Augustus and Agrippa.

But in the 19th century, it's people like Abate, who I mentioned before, working on Naples water supply, who finally say that they've they've started to reach the level of the Roman engineers and even go beyond it.

And so

the aqueduct that's built to supply Naples in the 19th century is not the repaired Roman one.

It's a completely new one.

And it's from that time on we start to see the science, the engineering of water supply in Europe moving beyond that Roman antecedent.

Only took them 1500 years.

That's a great way to end it, Duncan.

Absolutely fascinating.

It just goes to me to say, Duncan, Duncan, thank you so much for taking the time to come on the podcast today.

Oh, I've really had a great time.

Thank you, Tristan.

Well, there you go.

There was Dr.

Duncan, Keenan and Jones talking all things Roman aqueducts.

I hope you enjoyed the episode and let us know whether you'd like us to do more episodes in the future on other well-known types of Roman engineering of infrastructure, whether that be toilets, sewers, gardens, temples, bathhouses, you name it.

We'd love to hear your suggestions.

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That's enough from me.

I'll see you in the next episode.

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