The walls of Constantinople, built by Theodosius II in the fifth century, protected the city from invaders for more than a thousand years. At the beginning an early inner wall was erected by Constantine I, and the enlarged Constantinople was surrounded by a triple wall of fortifications, during the reign of Theodosius II. Built on seven hills, the city on the Bosporus presented the appearance of an impregnable fortress enclosing a sea of magnificent palaces and gilded domes and towers. In the 10th century, it had a cosmopolitan population of about 1 million.
Some ruins are still standing today...

Part of the inner walls of the city.
