Krems castle history dates back to the 11th or 12th century. It was built by the Archbishop of Salzburg and mentioned first time in 1248. In the 16th century it was expanded and remodelled in Renaissance style. After 1730 the castle lost its position as administration residence and was left to decay. Today Krems ruins are well preserved. A small museum room opened in May 2015 exhibiting the history of castle.
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.