A Brief History of the Aqueduct of Valens in Istanbul
What is the Aqueduct of Valens?
The Aqueduct of Valens is one of the largest aqueducts remaining from antiquity, and the most visible part of the monumental water system that supplied the city of Constantinople.
Aqueduct of Valens History
When a city has a large population and no natural fresh water it has a problem. Already in the 2nd century, the Roman Emperor Hadrian had built a smaller aqueduct to supply the town of Byzantium, but when Constantine made this small Greek fishing town the site of his new capital, demand quickly outstripped the supply of water. Much of the new city was also built at a higher elevation than the old, and until the advent of pumps and modern plumbing there was no way to get the water uphill except by carrying it.
It was clear they needed a new aqueduct. Aqueducts had long been part of the technology of the Roman Empire – some of the most famous still standing include the aqueduct of Segovia in Spain and the Pont du Gard in France. Vitruvius, the great Roman architectural theorist and military engineer, dedicated the entire eighth book of his treatise De architectura to the construction of aqueducts and water supplies. But Constantinople was a uniquely tricky prospect: there were just too few reliable supplies of fresh water even remotely within the vicinity of the city. Something extraordinary was demanded.
The aqueduct was completed during the reign of Emperor Valens in the mid-4th century; just how long construction took we have no idea. However, the project was vast. Archaeological investigation has uncovered channels bringing water from over 120 kilometres away in Pinarca to the city, and owing to the rocky and arid terrain, the water had to take a highly circuitous route: archaeologists have found 268 kilometres of gravity-led water channels. In the 5th century, a further 451 kilometres of channels were added to the system connecting further springs to the aqueduct. One problem with such an extensive network of channels beyond the city walls was that it was highly vulnerable to attack: the supply was cut by the Avars during the siege of 626 and seems to have run dry for a century until it was restored by Constantine V.
The most famous section of this colossal hydraulic system today is the Bozdoğan Kemeri (or ‘Aqueduct of the Grey Falcon’), which spans the valley between the Fourth and Third hills of the city. It’s 971 metres long and up to 28 metres high and consists of 86 arches. However, the feat of an aqueduct like this is not only in its gigantic size but its technical precision – the water needs to flow down a constant slope for a well-managed supply. The whole Aqueduct of Valens tilts at a steady decline of 1:1000, which means its height decreases by just a metre every kilometre!
All too often the Byzantine Empire is dismissed as technologically stagnant, in a steady state of decline from the heights of imperial Rome, but the Aqueduct of Valens is a counterargument to this narrative. It’s an extraordinary feat of engineering and the culmination of the longest water supply system known to us from the entire ancient and medieval world.