Introduction to the Istanbul City Wall: Designated as one of the World Cultural Heritage Sites by the United Nations Educational, Scientific and Cultural Organization, it extends 7 kilometers from the Strait of Marmara to the Golden Horn. It was first built by Theodosius II in the 5th century. It was built during the period and has been repaired many times since. The city wall in the old area is 7.2 kilometers long and has two layers. The inner wall was built in 413 and the outer wall was built in 447. It is surrounded by a city wall. The inner wall is higher, about 9 meters and 4.8 meters thick. The city wall is covered with Watchtower. The watchtower is 18 meters high and 54 meters apart. There were 92 turrets on the outer city wall, 56 of which still exist today. The city wall by the sea was built in 439. The city wall along the Golden Corner is 9 meters high and made of stone. There were originally 110 watchtowers and 14 city gates, but only a small part remains today. The city wall stretched for 8 kilometers along the Marmara coast, and most of it still exists today.