Recent excavations around the town, for example the Dyke Hills iron age ramparts and burial grounds tend to suggest that the Saxons were in the area before the Romans left.
By the time the Saxons had been there for some time they were referring to themselves as Dorsaetas and to the town as Domwaracester, cester being the Saxon word for Roman fort. The town thrived under the Saxons.
Christianity came early to Dorchester and a bishopric, which became Dorchester Abbey, was first established in the area around 635 and was the first one recorded in what was then the kingdom of Wessex. The bishopric was moved to Winchester in 690 and during the coming of the Danes in the late ninth century, was moved back to Dorchester.
After the coming of the Normans the bishopric was transferred to Lincoln by William the Conqueror in 1071 and the bishopric eventually became an Augustinian Abbey as recorded in the Domesday Book of 1086.