Demir Kapı, the Iron Gate, is the ruin of a sixth-century dam and arch built to control flash floods from the ravine above Antioch. City walls were later added over it, turning practical engineering into part of the defences.
The 2023 earthquake left the site more unstable, so treat it as a careful-look stop rather than a casual scramble. The view back over the city helps explain why ancient Antioch needed protection from both hills and water.