In 1069, after recognising the defensive qualities of Seresberi, now known as Old Sarum, William the Conqueror built a motte-and-bailey castle within an older Iron Age hillfort known as Sorviodunum, constructed around 400 BC.

[2] The courtyard was added around 1100 by Bishop Roger[3] and he also began work on a royal palace during the 1130s, prior to his arrest by Henry's successor Stephen.

[8] In 1171, King Henry II ordered that improvements be made to Old Sarum, including a new gatehouse, drawbridge, inner bailey walls and a treasury to be constructed within the keep of the castle; this work continued until 1189.

After these repairs and maintenance works, a new hall, kitchen, and bakehouse for the sheriff of Wiltshire were begun about 1201 and completed by 1215.

That protection has subsequently continued, expanding to include some suburban areas west and south-east of the outer bailey.