Dalarö fortress was built by Charles X Gustav of Sweden in 1656. It replaced an old structure from 1623. In 1683 the fortress was renovated by Erik Dahlbergh and the renovations were completed in 1698. The fortress has never been under siege and therefore well-preserved. It was decommissioned by the military in 1854. Today the building is a museum and it contains a restaurant.
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.