The famous classic Roman arches of the aqueduct of Constantinople still stand in Istanbul today, with it’s most prominent section largely intact. The structure has been maintained due to its impressive construction and continued usage and maintenance throughout the Roman/Byzantine and Ottoman eras.
The 4th century aqueduct of Valens is seen today as the robust bridge of arches that remains in Istanbul. It was in fact part of a much larger network to bring water to the metropolis of Constantinople. In addition to its vast network of cisterns, this was how Constantinople quenched its thirst. The city truly needed the aqueduct network when it’s population was high. During Late Antiquity many cities began a decline in population, especially in Western Europe. However, Constantinople actually grew during this time all the way until the plague of Justinian decimated the population of the city. Part of the reason the city was able to sustain such growth was its defenses, making it secure and able to grow unscathed by enemies, but also the aqueduct network which gave the population the water they needed to live.
The main water source for the aqueduct was over 120km or 75 miles away. Another smaller water source 15km away fed into it supplementally. The Anastasian wall project, which was a Hadrian’s Wall type of attempt to guard Thrace had protecting this water supply in mind as one of its major considerations. The actual aqueduct system was very complicated and expanded over time since the days before it was Constantinople, and was not all constructed by Valens even though this famous section was.
Nikalaos Mesarites in his description of the Holy Apostles Church described the gifts that the aqueduct gave the city’s residents where the water was plentiful. “Indeed one can see in it and in the regions surrounding it inexhaustible treasures of water and reservoirs of sweet water made equal to seas, from which as though from four heads of rivers the whole City of Constantine receives its supply. One can also see deep and fertile soil, rich and soft, easy to dig, richly responding to the desires of husbandmen, equally good for sowing and for growing, and well suited to the production of both classes of products, both tall trees with rich fruit, and fruits in abundance; the beauty of these even surpasses the quantity, and the crops are taller than trees themselves are elsewhere.“
The aqueduct stopped supplying water in 626 when the Avars cut it during the siege of Constantinople to help put pressure on the defenders. A sign of the tough times the Romans were going through during this era was that it was not until 758 the aqueduct was restored by orders of Constantine V. The Balkans were overran by Avars and Slavs, and the Bulgars, while the Arabs swallowed all of the provinces in Asia outside of Anatolia. The lack of water probably contributed to population decline in Constantinople in this time, and as the population rebounded the need for the aqueduct was returned.
During the Fourth Crusade and subsequent Latin occupation of Constantinople, the aqueduct system collapsed. Like most everything they touched, it went to ruin without the extensive maintenance required. The city’s population plummeted during that time and surely lack of water contributed as the hundreds of thousands of people of 12th century Constantinople could not survive only on cisterns. After 1261 the city never even close to recovered its population or prosperity, and the Romans had no resources for aqueducts. To illustrate the need for this aqueduct to maintain a large population, Mehmed II immediately made plans to restore this aqueduct after conquering the city as part of his plan to turn Constantinople back into a metropolis. The aqueduct of Valens was restored, but Mehmed had to extensively reengineer the ruined water channels of Thrace. Today’s aqueduct of Valens is, as often is the case, composed of many layers. It has ancient Roman, Byzantine, and Ottoman engineering.
The water supply of Constantinople: archaeology and hydrogeology of an Early Medieval city by P. Bono, J. Crow, and R. Bayliss
Nikolaos Mesarites: Description of the Church of the Holy Apostles at Constantinople. Edited by Glanville Downey
The Cambridge Companion to Constantinople, Edited by Sarah Bassett