The Hohensyburg, a castle complex of the Lords of Sieberg, was constructed on the grounds of a former Saxon refuge, which was conquered in 775 by the Franks under Charlemagne. The castle, which was built around 1100 of Ruhr sandstone, was partially destroyed in 1287 by Count Eberhard I. von der Mark. The castle complex was an imperial fief of the von der Mark counts from 1300. This fiefdom was transferred to Brandenburg in 1609, and later to Prussia.
Two keeps, residential quarters (two-chamber system), the wall ring and the walls around the courtyard complex are still recognisable. In the inside of the castle is a war memorial by Fritz Bagdons.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.