A quadrangular castle or courtyard castle is a type of castle characterised by ranges of buildings which are integral with the curtain walls, enclosing a central ward or quadrangle, and typically with angle towers. There is no keep and frequently no distinct gatehouse. The quadrangular form predominantly dates from the mid to late fourteenth century and signals the transition from defensively to domestically oriented great houses. The four walls are also known as ranges.
Bolton Castle, in England
Image: Beverston Castle
Image: Bodiam castle 10My 8 1197
Image: Bolton Castle
A keep is a type of fortified tower built within castles during the Middle Ages by European nobility. Scholars have debated the scope of the word keep, but usually consider it to refer to large towers in castles that were fortified residences, used as a refuge of last resort should the rest of the castle fall to an adversary. The first keeps were made of timber and formed a key part of the motte-and-bailey castles that emerged in Normandy and Anjou during the 10th century; the design spread to England, Portugal, south Italy and Sicily. As a result of the Norman invasion of 1066, use spread into Wales during the second half of the 11th century and into Ireland in the 1170s. The Anglo-Normans and French rulers began to build stone keeps during the 10th and 11th centuries, including Norman keeps, with a square or rectangular design, and circular shell keeps. Stone keeps carried considerable political as well as military importance and could take a decade or more to build.
The Norman (c. 1126) keep of Rochester Castle, England (rear). The shorter rectangular tower attached to the keep is its forebuilding, and the curtain wall is in the foreground.
Reconstructed wooden keep at Saint-Sylvain-d'Anjou
The Norman keep at Colchester Castle in Essex, built in a Romanesque style on the foundations of a Roman temple
The Norman keep (r) and prison (l) at Goodrich Castle, built to a square design in the early 12th century