Adulterine castle

Adulterine castles were fortifications built in England during the 12th century without royal approval, particularly during the civil war of the Anarchy between 1139 and 1154.

During the civil war of the Anarchy, fought between the factions of Stephen of England and the Empress Matilda, both sides built a number of new castles to defend their territories and act as bases for expansion, typically motte and bailey designs such as those at Winchcombe, Upper Slaughter, or Bampton by the Empress's followers.

[1] Similarly, Stephen built a new chain of fen-edge castles at Burwell, Lidgate, Rampton, Caxton, and Swavesey – all about six to nine miles (ten to fifteen km) apart – in order to protect his lands around Cambridge.

[3] Traditionally the King retained the right to approve new castle construction, but in the chaos of the war this was no longer the case.

[5] Robert of Torigny recorded that 375 were destroyed (slighted), without giving the details behind the figure; recent studies of selected regions have suggested that fewer castles were probably destroyed than once thought and that many may simply have been abandoned at the end of the conflict.