Early Norman castles like this were originally timber structures. Most were subsequently rebuilt in stone once Norman rule had been firmly established.
Given that there is no sign of Cranborne having been rebuilt, it presumably fell out of use once the surrounding area had been subdued. It was probably abandoned at the beginning of the thirteenth century, when King John built a hunting lodge in the centre of the village where Cranborne Manor now stands.
The castle consists of a circular motte, some 180 ft (55 m) in diameter and 28 ft (8.5 m) high.
This is surrounded by a crescent-shaped bailey, which on its eastern side has a rampart that is up to 25 ft (7.6 m) high in places, together with an outer ditch. The bailey is protected by the steep sides of the hill on the other sides.
The Dorset Countryside Service, together with the Edmondsham Estate which owns the site, have undertaken extensive clearance work in recent years; just as well, as the castle was almost lost in the undergrowth until recently.