Hovedøya Abbey was a Cistercian founded on 18 May 1147 by monks from Kirkstead Abbey in England on Hovedøya island, and dedicated to the Blessed Virgin Mary and Saint Edmund. A church dedicated to Edmund already stood on the island, and the monks took this over as the abbey church, modifying it to meet Cistercian requirements. The rest of the monastery follow a modified Cistercian building plan, to take into account a small local hill. The church itself is built in Romanesque style; the rest of the monastery was presumably Gothic. During the medieval period the abbey was one of the richest institutions in Norway, holding over 400 properties, including a fishery and timber yards.
Political turmoil during the succession to the throne of Denmark-Norway led to the end of the monastery. The abbot, having supported the Protestant King Christian II, possibly in a bid to gain support in the face of the coming Reformation, came into conflict with the commandant of Akershus Fortress, Mogens Gyllenstierne, who ironically had supported the Roman Catholic Prince Frederick I. In 1532 the abbot was thrown into prison for his political involvements, and the abbey was looted and then set ablaze, thus ending 400 years of monastic activity at Hovedøya. Any hope the order might have had in restoring the rich abbey was dashed 4 years later, when the Reformation swept over Denmark-Norway.
The site was later used as a quarry for stone for Akershus Castle. The remaining ruins are nevertheless among the most complete of a medieval Norwegian monastery.
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.