The square tower is the oldest part of the Château du Colombier but the exact date of construction is unknown. It was enlarged during the 13th and 14th centuries. In 2001-2002, the opening of the Hall of Frescos completed the tour of the chateau and allowed visitors to experience the refinement of its Renaissance decoration (XVI century)
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.