Rabenstein Castle was built around 1100 to protect nearby Sankt Paul im Lavanttal. It began as a mere watchtower built on a tall hill. Rabenstein became a castle when Engelbert I Sponheim, Margrave of Istria founded St. Paul's Abbey in 1091 in order to protect the abbey and town around it. The castle was occupied by the Rabensteins (whose name henceforth stuck to the structure) until 1200, the Archbishop of Salzburg until 1300. in 1636 the castle was destroyed by fire and left to decay.
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.