Dorchester Castle was a motte and bailey castle in the market town of Dorchester, Dorset, southern England. The date that the castle was built is unclear. Between 1154 and 1175 it was in possession of the Earl of Cornwall and it had become a royal possession by 1185. Both Henry III and John spent money on the castle. It appears to have been disuse…Dorchester Castle was a motte and bailey castle in the market town of Dorchester, Dorset, southern England. The date that the castle was built is unclear. Between 1154 and 1175 it was in possession of the Earl of Cornwall and it had become a royal possession by 1185. Both Henry III and John spent money on the castle. It appears to have been disused from about 1290 and there are references to its stonework being reused by the Chidlock family to build Dorchester Greyfriars in 1309. Certainly it was abandoned by 1422.