Guthrum (d. ca. 890) christened Aethelstan, alias Gorm in Danish, was King of the DanishVikings in the Danelaw. He had killed the Danish king some time before 854; subsequently, he waged a long war against Wessex and its kings, most notably Alfred the Great. By 878 he stood on the brink of a final conquest of Wessex but was decisively defeated by Alfred at the Battle of Edington, following which he was forced to sign the Treaty of Wedmore, in which he accepted Christianity and consented to the division of England into two kingdoms: Alfred's Wessex and his own Danelaw.
This was terminated by the peace of Wedmore in 878, when the Danes withdrew from Wessex and settled finally in East Anglia under their king Guthrum.
This peace was finally and definitely ratified in the document known as the peace of Alfred and Guthrum, which is probably to be referred to the year 880.
From this point the boundary is left undefined, perhaps because the kingdoms of Alfred and Guthrum ceased to be conterminous here, though if Northamptonshire was included in the kingdom of Guthrum, as seems likely, the boundary must be carried a few miles along Watling Street.