Kalø Castle was founded in 1313 by the Danish king Erik Menved in order to establish a stronghold in northern Jutland to counter the ongoing rebellions by the local nobility and peasants against the crown. The castle was successful and from the 15th century and onwards the castle had a more peaceful role as the local administrative center. King Christian II held the future Swedish king Gustav Vasa captive at Kalø during 1518-1519, until he escaped.
When king Frederick III converted the elective monarchy into an absolute monarchy by the revolution of 1660 in Denmark, the castle lost its function. In 1661, Frederick III gave Kalø to Ulrik Frederik Gyldenløve, who in the following year (1662), tore down the now abandoned castle. The material was used to build his private palace in Copenhagen, now called the Charlottenborg Palace. Today the castle ruin is owned by the Danish State.
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.