The English conquests of the later seventh century were soon followed by the establishment of a bishop’s see at Sherborne, for Wessex west of Selwood, of which Aldhelm was the ﬁrst bishop (705). Originally this had a house of canons attached, and these were not replaced by monks till 998. About the same time as the cathedral a double monastery, with separate houses for monks and nuns, was founded at Wimborne by Cuthburga, sister of King Inez such houses were a regular feature of the early Saxon Church, and were generally ruled by abbesses of royal descent. Wareham also had a nunnery at some early date, but it seems to have been destroyed when the Danes occupied the place in 876.
After a century and more of peace, in which the English settlers busily pioneered their new villages in the valleys, warning of trouble came with a raid of Norwegian Vikings on Portland about 795. This was the ﬁrst attack on Wessex, and one of the ﬁrst on England, and no—one yet realised the danger. The king’s reeve rode out from Dorchester to enquire their business, and was killed. Forty years later Danish Vikings began to swarm in the Channel, and in 836 they landed at Charmouth and defeated Egbert of Wessex. Shortly afterwards they appeared again in Portland, where they killed the ealdorman of Dorset, and in 843 they made a second descent on Charmouth. At this stage, however, their object was only to plunder and sail off with the spoils.
The real invasion came in 876, when Guthrum tried to follow up his conquest of East Anglia with that of Wessex. The plan was well-organised: Wareham, situated between two rivers in a position which could be easily defended and used as a base, was seized by a Danish army marching overland, while ships concentrated in Poole Harbour from east and west in support. Much of the surrounding country was plundered before Alfred came up to blockade Wareham, and he had neither the strength to take it by assault nor the ships to cut it off by sea. He offered Guthrum free passage in return for a promise to leave Wessex, but the Viking broke his oaths and made a dash for Exeter instead. Much of the Danish ﬂeet, however, perished in a storm off Swanage on its way to join him there. Alfred’s ﬁnal battles to save Wessex had yet to be fought, but Dorset was not again directly troubled.
As part of his plans to prevent further Viking attacks, Alfred organised burhs (forts of earthwork and Stockade) to be rallying points for the forces of their district and to block rivers up which Danish ships might penetrate inland. Dorset at ﬁrst had three, closing the main approaches. Wareham guarded the mouths of the Frome and Piddle, and Bridport the chief route into the west of the county, while Shaftesbury was one of a line of inland forts westwards from Winchester. Twineham (now Christchurch) in Hampshire blocked the Dorset Stour as well as the Hampshire Avon. Dorchester seems not to have been among the original burhs, but its central position and its remaining Roman walls soon made it one. All four Dorset burhs had moneyers striking silver pennies in late Saxon times.
Shaftesbury Abbey was founded by King Alfred after he had defeated the Danes, and several more followed in the peaceful times of the great tenth century kings. Milton was a foundation of King Athelstan, and Cerne, Cranborne, and Horton of Wessex noblemen.
The second Danish Invasion, of Ethelred’s time, was more disastrous to Dorset than the ﬁrst. The monastery of Wimborne was destroyed, to be later refounded as a house of canons only, and the abbeys of Cerne and Horton were both plundered – Cerne by Canute. The heavy Dangeld taxes, raised year after year to pay off marauding armies, drove many men to give up their freedom and seek the protection of a lord. But once Canute was established as king he became a pious Christian with surprising rapidity; and in 1026 his steward Orc, following his master’s example, founded at Abbotsbury a house of canons which was soon afterwards reorganised as a Benedictine monastery. This brought the number of Dorset abbeys, apart from Wimborne, to eight — an exceptional ﬁgure at a time when Sussex had none at all.