Colgrim invaded Britain in the early days of Arthur’s reign. Arthur defeated him at the river Douglas and pushed him back to York, where he was saved by the arrival, from Germany, of Duke Cheldric and another brigade of warriors.
Arthur returned to defeat Colgrim’s army in the forest of Caledon and at Lincoln (some want to make these one battle), and the Saxons agreed to return to Germany. They broke the treaty, however, and sailed south to conquer Totnes. They marched north, ravaging the land, and besieged Bath. Arthur arrived in Bath and killed Colgrim and Baldulph.
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
Roman de Brut | Wace, c. 1155