The 'Digtionary

Hill fort

Hill forts start to appear on high ground in the late Bronze Age but explode in numbers during the Iron Age. Some are quite small with a single ditch and bank, whereas others have multiple massive banks and ditches as well as complex entrance arrangements. Traces of wooden palisades on top of the banks are common, and some like Barbury Castle fort (just north of Marlborough) were further reinforced with stone. Most excavations show multiple roundhouses inside and some forts like Old Sarum became sites for Roman settlements or were re-occupied in the post-Roman period.

Keep

The keep is the central defensive building of a medieval castle as seen at Old Sarum and Farnham.

"The route starts and ends in Winchester where Alfred is buried, and connects iconic monuments including Stonehenge, Avebury stone circle, Iron Age hill forts, Farnham Castle, and Winchester and Salisbury Cathedrals."

Motte and bailey

The classic Norman castle puts a timber or stone keep stronghold on top of a motte or mound. This is then surrounded by a larger bailey protected by a ditch and bank/ramparts. Again, Old Sarum and Farnham are great examples.