The situation described did not happen immediately. In 538 BC, Cyrus, the ruler of the Medes and Persians, took over Babylon. He left the walls and city of Babylon in place. The enormous bloodbath, as described in Isaiah 13, did not happen at that stage. The prophecy cannot be limited to one specific time. The fulfillment thereof happened in various stages, of which the conquest by Cyrus was only one. In 518 BC, Darius Hystaspes conquered the city and destroyed the walls. By the last century BC, nothing except ruins remained of Babylon.
20 It will never be inhabited or lived in for all generations; no Arab will pitch his tent there; no shepherds will make their flocks lie down there.