Roman Aqueducts

The typical image of a Roman Aqueduct is a massive arched structure carrying a river of water hundreds of feet overhead to the city. While these sections of aqueducts do exist, most of the Roman aqueducts were underground tunnels that carried water inside. For example, the first Roman aqueduct, the Appian, was built in 331 BC.1 The Tiber river was no longer sufficient to meet the needs of Rome. The Appian carried clean spring water 10.2 miles into the heart of Rome. By 144, the population of Rome had doubled and the Marcia aqueduct was built to deal with the increasing demand for water. Both of these aqueducts were nearly all underground with only a small percentage of the total length being above ground.

One of the best primary sources for aqueducts comes from Frontinus in 97 AD. He was appointed to the position of water commissioner for Rome. To prepare himself for this job he learned about all of the aqueducts and wrote two books on the topic.1 In his two volumes, Frontinus give the details about each one of the 9 aqueducts present at the time of writing. He goes over the story of each one, recording when it was made, where it sourced water, how long it was, and when it was repaired. He also addresses the laws regarding the tapping of aqueducts for personal use. Water was typically stolen by taking pipes and pounding them through the walls to drain off the water. This would cause damage to the aqueduct allowing water to leak out. Other causes of damages included trees roots breaking apart the tunnels, sediment buildup, deposits coating the channels, and storms.

Typically Romans tried to build the aqueducts underground, but when there was a valley that needed to be crossed, the Romans came up with a couple different solutions. A common way to cross small valleys was to create a bridge across them. However, if the valley was too large for a bridge to be practical, the Romans used a technique called the inverse siphon.2 They would run a lead pipe down through the valley and up to the other side. The pipe was watertight so as long as the side closest to the source was higher than the other side, water would flow through the pipe and get pushed back up due to the pressure from gravity in the pipe.

Distribution Center2

Along the path of the aqueduct, settling tanks were placed to allow the water to slow down and drop out dirt and rocks that were swept along the channel. As the aqueduct reached the city, screens filtered out debris in the water. Then, the water would flow into a distribution center. These had an inlet for the water from the aqueduct and a few outlets that led to different parts of the city. They could be for private use, public fountains, and baths. The outlet channels would be at different heights where the higher the channel, the earlier water to it would be cut off in the case of a drought. This was an ingenious way of making sure people could get access to drinking water even in the case of a water shortage.

Making Lead Pipes2

From these distribution centers, the water flowed through underground lead pipes to its destination. The pipes were made by pouring molten lead into a sheet, letting it cool, bending it into a cylinder, and welding the top seam with more molten lead. The pipes were then buried under the main streets leading to more distribution centers, baths, fountains, or straight into people’s homes.

With all of the lead making up the Roman water system, it is natural to wonder if they suffered from lead poisoning. However, the lead pipes used to carry water most likely did not raise the concentration of lead in the Roman water to an unsafe level. There are two main reasons for this. The first is that water was always running through the pipes. The fountains and baths were designed to overflow into sewers that carried the dirty water away. The lead would have very little time to contact the lead pipes, so not much lead would be able to dissolve. The other reason is indicated in Frontinus’ books. The water would leave deposits of calcium carbonate lining the walls of the aqueducts and more importantly the lead pipes. After enough deposits had built up, the lead would no longer be in contact with the lead anymore.1

Running water was the key to Rome’s large population. At its peak, the population of Rome is thought to have risen to one million people. One of the reasons Rome was able to have such a large population, was because waste and disease were washed away from the city by the constantly running water. Aqueducts supplied water for drinking, cooking, bathing, and cleaning to hundreds of thousands of Romans every day. It is because of the combination of their beauty and usefulness that Frontinus says the following about them.

“With such an array of indispensable structures carrying so many aqueducts, compare if you please, the Pyramids, or the famous but useless works of the Greeks”

Frontinus1
  1. Frontinus, Sextus Julius, Charles E. Bennett, Mary B. McElwain, Clemens Herschel, and Sextus Julius Frontinus. The Stratagems: and the Aqueducts of Rome. The Loeb classical library, LCL 174. Cambridge, Mass: Harvard University Press, 1993.
  2. Hodge, A. Trevor. Roman Aqueducts & Water Supply. London: Duckworth, 1992.
  3. “Aqueducts: Quenching Rome’s Thirst.” History Magazine, November 15, 2016. https://www.nationalgeographic.com/archaeology-and-history/magazine/2016/11-12/roman-aqueducts-engineering-innovation/.

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