Gävle Castle is the northest one of so-called Vasa castles, built by Gustav Vasa of Sweden or his sons. The construction started in 1583 by the religious King John III of Sweden. The design was made by Willem Boy and the center of castle was a chapel. The castle was completed in 1597, five years after John's death.
In 1727 the chapel and the top floor were destroyed by fire. Gävle castle stayed damaged until 1741, when it was agreed to rebuilt. The current appearance dates from the design made by Carl Hårleman. In 1754 the reconstruction was complete.
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.