Sometime between May 6-12, 878, at the Battle of Edington, Alfred the Great and his West Saxon army defeated the Viking army of Guthrum the Old. A short excerpt from the article:
"The Saxon fyrd lined up in shield wall formation. In a fiercely fought battle that lasted throughout the day, the Saxon forces wore down the Danes. Alfred pursued them back to Chippenham, trapping them in his fortress there. Asser's Life of King Alfred relates -
"Fighting ferociously, forming a dense shield-wall against the whole army of the Pagans, and striving long and bravely...at last he gained the victory. He overthrew the Pagans with great slaughter, and smiting the fugitives, he pursued them as far as the fortress'
After fourteen days the Vikings sued for peace. Alfred realised that he could not realistically hope to drive the Vikings out of the rest of England. The best he could hope for was to consolidate his current possessions.
By the terms of the peace agreement, known as the Peace of Wedmore, Guthrum agreed to withdraw to territory already under Danish control, that is, behind Roman Watling Street. Guthrum accepted Christianity and was baptized, taking the name of Aethelstan, with Alfred standing as sponsor. To render thanks for his victory, Alfred founded Athelney Abbey on the island in 888. The Abbey survived until the Dissolution of the Monasteries under King Henry VIII in 1539."