The Rise and Fall of the Roman Aqueduct
What did the Romans ever do for us? The very fact they still intrigue us should put this question to bed. And in terms of engineering, they did quite a lot. Let's take one prime example of revolutionary engineering: Roman aqueducts.
If you travel around Europe and the Middle East, you'll quickly run into examples of aqueducts. Some are even still completely serviceable. The Trevi Fountain in Rome still gets fed by an ancient aqueduct (even though it's now pressurized).
Did you know?
Mention aqueducts and most people will instinctively think of a large stone bridge, perhaps arched, that carries or once carried water along its course.
Aqueducts are a complex network of ground works, pipes and other structures designed to transfer water from a source to a destination. It's not just the iconic stone structures seen today. For the most part, aqueducts transport water long distances simply under the influence of gravity - absolutely simple but ingenious. These are in fact merely conduits to the aqueduct system.
[ Image Source : Graphics reporting by Tom Kington. Graphic by Doug Stevens/LA Times ]
The First Aqueducts
Aqueducts are not unique to Ancient Rome. Many other civilizations developed similar engineering. Crete has early examples of simple water channeling systems from the Minoan period. Egypt and China both had their "quanats" to carry water underground. Even ancient Aztec culture had versions of this technology.
The first long-distance canal systems were constructed by the Assyrians in the 9th century BC. In the 7th century BC Assyrian king Sennacherib constructed a wide canal with a 920 ft (280 m) long white stone ‘bridge’. This was used to bring water to Nineveh via the Jerwan aqueduct, which is acknowledged as the first large above-ground aqueduct.
The Greeks, not to be outdone, built aqueducts to supply Athens, amongst other locations, via long distance aqueduct systems in the 6th century BC.
When in Rome
Before aqueducts, Romans relied on local water sources such as springs and streams. These were supplemented by groundwater from privately or publicly owned wells. Seasonal rainwater was also exploited by draining from rooftops into storage jars and cisterns, much like rainwater harvesting today. The reliance of ancient communities on these water resources restricted their potential growth.
By the early Imperial era, Rome's aqueducts supported a population of over a million. They also supplied extravagant water supply for public amenities such as baths, fountains and latrines.
[ Image Source: PaperBlog ]
Before building an aqueduct, Roman engineers assessed the quality of a potential water source by examining: the water's clarity, source rate of flow, and taste of the water. They also took note of the physical condition of the locals who drank it. Once a site was approved, surveyors calculated the right path and gradient for the conduit, as well as its channel size and length.
Springs served as the most common sources for the aqueduct. However, some aqueducts got water from dammed reservoirs like the two still used in the provincial city of Emerita Augusta. Roman engineers used a number of different tools to plan the aqueduct's construction. Horizons were checked using "chorobates," a flat-bedded wooden frame fitted with a water level.
The aqueducts themselves ran 0.5 to 1 m beneath the ground's surface. While early aqueducts were made from ashlar, late Republic-era Rome used brick-faced concrete for a better seal. Contemporary Roman engineers such as Vitruvius recommended a low gradient of not less than 1 in 4800 for the channel. This was presumably to prevent damage to the structure.
Failing to plan is planning to fail
Once built, aqueducts had to be maintained and protected. The city of Rome at one time employed about 700 maintenance personnel for this purpose. The excellent planning of the ancient Romans ensured that maintenance requirements were incorporated into the design.
For instance, underground sections of the aqueducts were made accessible by means of manholes and shafts. When major repairs were needed, engineers could temporarily divert the water away from a damaged section.
Notable Roman Aqueducts
The combined conduit length of the aqueducts in the city of Rome is estimated between 490 to a little over 500 miles. 29 miles (47 km) of which was carried above ground level, on masonry supports. It is estimated that Rome’s aqueducts supplied around 1 million cubic meters (300 million gallons) a day. That's a capacity of 126 percent of the current water supply of the city of Bangalore, which has a population of 6 million – amazing!
The longest Roman aqueduct system is believed to have been in Constantinople. What's known of the aqueduct runs two and a half times longer than the ones found in Carthage and Cologne. Many scholars believe it to be the most outstanding achievement in pre-industrial societies.
Perhaps the second longest, built in the 2nd Century, the Zaghouan Aqueduct is 57.5 miles (92.5 km) in length.
["Aqueduct of Segovia" courtesy of Bernard Gagnon/Creative Commons ]
After the fall of the Roman Empire, aqueducts were either deliberately vandalised or fell into disuse through lack of organised maintenance.
This was devastating for larger cities. Rome's population declined from over 1 million in the Imperial era to 100-200,000 after the siege of 537 AD. Observations made by the Spaniard Pedro Tafur, who visited Rome in 1436, reveal misunderstandings of the very nature of Roman aqueducts:
"Through the middle of the city runs a river, which the Romans brought there with great labour and set in their midst, and this is the Tiber. They made a new bed for the river, so it is said, of lead, and channels at one and the other end of the city for its entrances and exits, both for watering horses and for other services convenient to the people, and anyone entering it at any other spot would be drowned."
It is a real testament to Roman engineers that some of their aqueducts are still in use some 2000 years later. They have become iconic structures in their own right and modern aqueducts, for the most part, would not be unrecognizable to ancient Romans. That’s quite a feat.
Featured Image "Aqueduct of Segovia" courtesy of Bernard Gagnon/Creative Commons
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