It is built on the site of an 11th-century defensive structure. A caponier is a type of defensive structure in a fortification. The old fort was rebuilt into a defensive structure. The construction of the medieval defensive structure of Milan started in 1156. A ringwork is a form of fortified defensive structure, usually circular or oval in shape. One of the Junta's projects was the construction of a new defensive structure at Almeida. It remained a defensive structure up until the 13th century. The main defensive structure is a revetted lunette shaped earthwork. As a defensive structure, palisades were often used in conjunction with earthworks. It was damaged by fire and rebuilt, and may have been a defensive structure. The three-storey keep was primarily a defensive structure. The remains of the north gate show an imposing defensive structure. There was no wall around the post, and the only defensive structure was a blockhouse. This defensive structure built of sandstone from Bray was built around 1358. The Broad Wall is a massive defensive structure, seven meters thick.