Christiansholm Fortress was finished in 1672 and formed a part of King Christian IV's plan for defense of Kristiansand when the city was founded in 1641. The architect of the fortress was quartermaster general Willem Coucheron. It was built on an islet, about 100 yards from shore. Today the fortress is connected to the mainland.
The only time the fortress has been in battle was against an English fleet force, lead by HMS Spencer (1800) in 1807 during the Napoleonic Wars. It was decommissioned by royal decree during June 1872 as part of a major redevelopment of fortifications across the nation.
Today, Christiansholm is a tourist attraction by the Kristiansand Boardwalk and venue for a variety of cultural events and festivities. It is now owned by the municipality and is a site used principally for recreation.
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.