After the withdrawal of the Roman army in 410 AD the Romano-Britons continued to live in Sorviodunum until the Saxons arrived in the 6th C. After consolidating their position between Southampton and Downton in the first half of the century they eventually launched an attack on the hill fort in 552. The Anglo Saxon Chronicle states, "In this year Cynric fought against the Britons in the place which is called Searobyrg (or Searoburh) and put the Britons to flight". Unfortunately there is very little archaeological evidence from the sub-Roman and early Saxon period at Old Sarum.
However, in the later Saxon period, when the Vikings were marauding the coastal areas of British Isles, the defences of Old Sarum were refurbished. King Alfred (871 - 899) issued an order to Leofric, Earl of Wiltonscire in 871 to preserve the castle of Sarum and to make another ditch defended by Pallisades. This ditch is the second ring and exhibits classical late Saxon characteristics. Searobyrg had become a place of some importance. King Edgar (943 - 975) held a Council at Searobyrg in 960. The Anglo Saxon Chronicle records for 1003, "Swein led his army into Wilton and they ravaged and burnt the borough, and he betook him then to Sarisberie and from there went back to the sea". It's unlikely that Swein would have come to Old Sarum unless there was something worth pillageing. Soon after this event a number of moneyers from Wilton are found at Old Sarum minting coins during the reign of King Canute (1018 - 1035). This suggests that the area was a borough because, under the laws laid down by King Athelstan, mints were one of the attributes of a borough.
In the years immediately before the Norman Conquest Old Sarum seems to have been one of the two most important mints in the shire and probably one of its most advanced trading centres. It seems to have been entirely surrounded by a large estate, of some 9 sq miles, which was in the possession of the Bishop of Ramsbury and Sherborne.