The Iron Tower (Eisenturm) is a medieval tower dating to the early 13th century, and modified in the 15th century, which with the Wood Tower and the Alexander Tower is one of three remaining towers from the city walls of Mainz, Germany. Its name derives from the Iron Market (Eisenmarkt), which was held in the immediate vicinity until the 19th century.
The Iron Tower served as a watchtower and gate to the city, and later as a gaol. It was badly damaged in World War II and reconstructed in the 1960s. Today it houses various organizations and art projects and is used for art exhibitions.
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.