The position and the layout of Stahlberg Castle clearly indicate that it is founded in the 12th century. It is situated on a rocky projection to the northwest of the town. The ring wall, parts of which have been rebuilt, surrounds the whole area and is rectangular in shape with several openings. A prominent circular tower that rises next to the gateway like a keep was added at the start of the 13th century and secures the narrow entrance with its curtain wall and a ditch. This part of the design is based on a similar feature at Stahleck Castle. The original keep can probably be identified in the ruins of an angular tower in the upper part of the castle.
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.