Hammershus is Northern Europe's largest medieval fortification, situated 74 metres above sea level. Erected in the 13th century, it was long believed that the castle was built as a private residence for the archbishop of Lund. However, new evidence found at the ruins of the castle suggests it was constructed in the beginning of the century as a royal residence for Valdemar II of Denmark and a base for the Danish crusades, according to Kjeld Borch Westh, superintendent of the National Museum of Denmark.
During a number of successive struggles between the kings of Denmark versus the Archbishopric, the fortress, serving as a refuge for the Archbishops, e.g. Jens Grand, was conquered by the king's army on a number of occasions, e.g. 1259, 1265, 1319, and 1325. In 1521, it was taken by king Christian II who used it to imprison Bishop Jens Andersen Beldenak of Funen. The fortress was conquered by forces of Lübeck the same year.
In 1658, Hammershus was occupied by Swedish forces but a rebellion on the island terminated the Swedish rule. The rebels led by Jens Pedersen Kofoed shot the Swedish commandant Johan Printzenskiöld and the Danish peasants traveled to Copenhagen to return the island to the king of Denmark. Corfitz Ulfeldt and his wife Leonora Christina were imprisoned in Hammershus 1660–1661, and the fortress was used as a prison on several other occasions.
The fortress was partially demolished around 1750 and is now a ruin. It was partially restored around 1900.
The fortification consists of the base castle residence and accompanying Mantel Tower, and includes a great stonewall stretching 750 metres around the castle grounds. Bricks found at the tower during the renovation led Westh and other experts to revise their theory on when the structure was originally constructed, moving back the date from around 1255 to the beginning of the century, when Valdemar became king.
Visitors to Hammershus have a spectacular view of the coastline and the sea surrounding Bornholm. South of the castle is a deep valley, water filled hollows, and dense forest. There are numerous points before arriving at castle where enemies could be stopped. The castle was built with box-like rooms surrounded by rings of fortifications. Each provided an additional layer of protection from invaders. Two natural spring ponds provided fresh drinking water on the side of the castle. Hammershus Fortress features a 750-metre-long perimeter wall and features a grand tower called the "mantel" tower.References:
The city walls of Avila were built in the 11th century to protect the citizens from the Moors. They have been well maintained throughout the centuries and are now a major tourist attraction as well as a UNESCO World Heritage Site. Visitors can walk around about half of the length of the walls.
The layout of the city is an even quadrilateral with a perimeter of 2,516 m. Its walls, which consist in part of stones already used in earlier constructions, have an average thickness of 3 m. Access to the city is afforded by nine gates of different periods; twin 20 m high towers, linked by a semi-circular arch, flank the oldest ones, Puerta de San Vicente and Puerta del Alcázar.