Constantine the Great began construction in the year 324, the Walls of Constantinople completely surrounded the new city, protecting it from attack by land and by sea. Beginning at the Church of St. Anthony at the Golden Horn and running south and southwest to the Church of the Theotokos of the Rhabdos on the Propontis coast, the wall was reinforced with towers at regular intervals.
As the city expanded, new walls were built by the Emperor Theodosius II in the early 5th century about two kilometers west of the original Constantinian walls. The walls consisted of both an inner and outer wall, both made of limestone blocks. The inner wall was at least 5 meters thick and 12 meters high, while the outer wall was at least 2 meters wide and 8-9 meters high.
Over time both sets of walls were significantly damaged by earthquakes and floods and after the Latin conquest at the start of the 13th century, fell into a bad state of disrepair. Nonetheless, the walls remained intact through most of the Ottoman Period, but as the city outgrew its boundaries in the 19th century, sections began to be dismantled. A restoration project financed by UNESCO began in the 1980s, but today the walls are considered one of the most 100 endangered sites in the world.