These are the remains of the oldest known aqueduct in the world. The Jerwan Aqueduct was constructed by king Sennacherib I of Assyria between 703 and 690 BCE. It represents a great feat of Assyrian engineering.
The aqueduct was transporting water in a canal across another river, with the destination of Nineveh. Recent research suggests that this canal may have been used to provide water to the Hanging Gardens, which may have been in fact located in Nineveh and not in Babylon.