Sipoonlinna (Sibbesborg) was a medieval castle made of stone and wood. It was probably built in the 14th century as part of the fief system created by Albrecht von Mecklenburg. Regarding folklores castle was founded by viking Sibbe (Sighbion) or Danish crusaders in the 12th or 13th century. Nowadays only some earth walls remain on the forested hill upon which it stood. The site can be accessed on foot.
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.