Silesian Ostrava Castle was originally built in the 1280s near the confluence of the Lučina and Ostravice rivers. The castle was built for military purposes due to its proximity to the Polish border.
In 1534, the gothic castle was rebuilt into a renaissance chateau. It burned down in 1872 but was rebuilt. It was restored recently after many years of dilapidation, caused by coal mining under the castle. Today, the castle is one of the most important tourist attraction of the Ostrava city.
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.