Niederkastenholz castle is surrounded by a moat, with an angular main castle and a separate horse-shoe shaped fore-castle with working quarters. It used to belong to Kornelimünster Abbey. The rough stone buildings of the castle are complemented by the wrought-iron gate. The fortified tower dates back to the 12th century and is the oldest part of the castle.
The so-called Probstei was added onto the medieval main castle between 1752 and 1756. Part of the moat is still visible today, although most of it was filled in during the 19th century.
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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.