The two castles of Kleinvernich and Großvernich have guarded the eastern and western banks of the river Erft since 1350. The two-part Grossvernich Castle, known as a 'castrum' with a moat, was built after 1300 near the surrounding wall, which today is hardly discernible.
Kleinvernich Castle is still entirely surrounded by a moat today. However, the estate is used exclusively for agriculture. The only memorial to the late-gothic castle in Grossvernich is the ruin of a tower which is in danger of collapse.
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.