It is described by the historian Barbara Yorke as a "formidable natural obstacle" in the Anglo-Saxon period, which was a significant boundary between east and west Wessex.
It may earlier have been a negotiated frontier between Wessex and the British kingdom of Dumnonia which was important in the later development of the West Saxon shires, and later boundaries between Wiltshire and Somerset and north Dorset run through the forest.
The boundaries through the forest and Bokerley Dyke which separated Somerset and Dorset from eastern counties may date to the fifth or sixth centuries.
Their motives are not known, but one factor may have been resentment of western nobles at the favour Æthelwulf had shown to Winchester and its bishop in eastern Wessex.
According to Asser's Life of King Alfred: The Anglo-Saxon Chronicle refers to Selwood in describing the gathering of English forces to oppose a Viking attack in 893: Wessex was divided between two ealdormanries in the tenth century and Selwood marked the boundary between them, but it lost its importance when Godwin was appointed earl of all Wessex around 1020.