Constantinople Civil Architecture: Valens Aqueduct

Constantinople's lack of sufficient water resources forced the rulers to rethink the system of water supplies. The construction of the main aqueduct, a work of fine engineering, which brought the much needed water was finished by the emperor Valens in the 4th c. AD.
Here is a map with its location in modern Istanbul:

And some pictures: 

The aqueduct was a landmark of the city in Ottoman times as well: