Fort Rhijnauwen was built between 1868 and 1875 as part of the New Dutch Water Defence Line. Because of its architectural style and good state of preservation, the fort is historically unique. Due it was closed to the general public for years it became a paradise for many endangered plants and animals. There are also weasels, foxes, roe, grass snakes and many varieties of butterflies. In winter, hundreds of bats hibernate in the fort. The fort consists of bombproof shelters, powder magazines, barracks, flank defences, group shelters and a large practice and parade square. Surrounding the complex is a double moat. Today, the fort can be visited on a guided tour.
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.