history

The Roman Empire was famous for many things—its record-breaking longevity, its size, its emperors, its military prowess (for better and for worse) and its influence on Western civilization. But one of Rome's most impressive claims to fame is even greater than many of us realize—the incredible engineering of its aqueducts.

At some point in school, we all learned that the Romans built aqueducts to move water from place to place, and most of us probably thought, "Cool," before moving on to our algebra homework. But we may not have fully grasped just how cool the aqueduct system was or how mind-blowing the Romans' abilities were for the time period. Heck, modern water transport systems still use the same principles the Romans did, and the fact that some of the Roman aqueducts are still in use over 2,000 years later is a testament to their advanced understanding of materials and craftsmanship on top of their grasp of civil engineering.

Nicopolis Roman Aqueduct in GreeceJennikann/Wikimedia Commons

A two-minute video from Learning History Simply highlights what made the Roman aqueducts such an engineering masterpiece. It started with finding a water source with a higher elevation than the destination. The Roman army helped plot out routes as engineers determined the slopes necessary for gravity to do the work of moving the water.

While we often think of the aqueducts built above ground, most of them—approximately 80%—actually ran underground through channels lined with hydraulic mortar with occasional vertical drops to relieve pressure.

- YouTube youtu.be

Settling tanks were used to remove impurities, basically slowing the water down to a speed at which sediment was able to fall to the bottom of the basin. Aeration—allowing the water to flow through open air and fountains—also served to purify the water flowing to Rome by precipitating minerals, helping it taste better and remove odors. (However, according to Engineering Rome, it's unlikely that they knew of those benefits and just unintentionally reaped them through the open air sections of the aqueducts.)

To build the underground aqueducts, the Romans used a mining technique that involved digging a vertical shaft every 30 meters, which enabled them to work faster and check alignment as they went. When they hit valleys, they would build bridges with the aqueducts on top of it, like the famous Pont du Gard. Arches higher than 20 meters became unstable, so they created tiers stacked on top of one another to gain elevation. Deeper valleys were traversed with an inverted siphon system that involved a sealed pipe flowing down and then back up again using only gravity and pressure.

The Pont du Gard is a portion of a Roman aqueduct that supplied water to to cross the Gard river in what is now France.ChrisO/Wikimedia Commons

Another feature of Roman aqueduct engineering was sluice gates, which allowed them to stop or divert the flow of water. That came in handy for isolating sections to repair as well as for regulating pressure.

Finally, once the water arrived in the city, it was collected in a large distribution basin called the Castellum Divisorium. It was then split into different tanks at different heights—the lowest fed the public fountains, the second lowest for the thermal baths, and the top tier went to private homes. Then it was distributed throughout the city via a network of lead, wood, and terracotta pipes.

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How have the aqueducts lasted as long as they have? Scientists have long wondered what made Roman concrete so durable, and in 2023 some light was shed on the mystery. Essentially, they created self-healing concrete. Ancient Roman concrete contains white chunks, or "lime clasts," which had always been assumed to be simply sloppy mixing practices. Turns out, it may have been genius instead. The chemistry is a bit complicated, but essentially it appears that the Romans used a method of mixing their concrete with quicklime—lime in its more reactive form—at high temperatures. When cracks begin to form in the concrete, they do so in the lime casts first simply because they're brittle. But MIT News explains how those brittle casts actually self-heal:

"This material can then react with water, creating a calcium-saturated solution, which can recrystallize as calcium carbonate and quickly fill the crack, or react with pozzolanic materials to further strengthen the composite material. These reactions take place spontaneously and therefore automatically heal the cracks before they spread."

Augustus Caesar commissioned the first Roman aqueduct.Stephencdickson/Wikimedia Commons

And whom do we have to thank for the aqueduct system? Emperor Augustus (27 BC - 14 AD) commissioned the first aqueduct, but it was completed during the reign of Emperor Claudius (14—37 AD). The gentleman to whom its completion was entrusted was the Curator aquarum, or "water magistrate" of Rome, architect Marcus Vipsanius Agrippa. Rome would ultimately have 11 aqueducts bringing water into the city from as far as 92 km (57 miles) away, but there were hundreds of kilometers of aqueducts throughout the full empire.

Understandably, people are still impressed by the engineering of Roman aqueducts:

"I mean, having an aqueduct so good it lasts 2000+ years and it's still in use has to be in the top 10 flexes of all time."

"Unimaginable how much work must have gone into a project like this. Breathtaking display of human ingenuity. Respect to our ancestors."

"The Romans were incredible engineers. Not only did they come up with the ideas but had the ability to carry them out."

"I’ve spent all my life in construction sites and I could not imagine the effort and man power a project like this could take. Simply impressive work."

"As someone who works in the water industry… it’s absolutely crazy to me how many of these techniques and processes we use even today on modern site, almost the exact same as they did all those centuries ago, ingenuity at its finest from the Romans."