The Theodosian Walls of Constantinople in Istanbul, Türkiye

This is a walk along the entire 5.7 km/3.5 mile length of the walls that protected Constantinople for more than a thousand years, from the Golden Horn to the Sea of Marmara. These walls were built by Byzantine Emperor Theodosius II in the 5th century AD. They were the last great fortification system of antiquity, and are one of the most complex and elaborate systems of city walls ever built.