The origins of the vast mound on which Old Sarum stands are unknown but the Romans, who called it Sorbiodunum, made it the hub of their roads to Bath, Dorchester, Silchester and Winchester. The Saxons named it Searisbyrig after their own fashion and King Edgar held a Council here in 960. The Danish King Sweyn attacked Searisbyrig and burned it in the early 11th century and his son Cnut, more popularly known as Canute, is reputed to have died here in 1035.

Sarum superceded Sherborne to the west as the see in 1075 and it was under the second bishop here, Osmund (1078-99, a nominee of William (the Conqueror) I), that the cathedral church here was completed.

It was also during the time of The Conqueror that the great ditch in the north-western quarter was dug and the castle erected there as a stronghold from which to enforce Norman rule on the surrounding country.

With the departure of the church and clerics from the site in the 12th century and the abandonment of the fortifications in the 14th century, the site became all but delerict save for a few houses. Despite this it retained the privilege of returning two members of parliament until the passing of the Municipal Corporations Act in 1832 - and Act designed to deal with just such 'Rotten Buroughs'. So valuable was the right to nominate two members considered to be that ownership of this small estate was said to have changed hands for a staggering £ 60,000. The elections took place in a field where the last few houses of the borough stood.