In August 937, Olaf sailed from Dublin with his army to join forces with Constantine and Owen and in Livingston's opinion this suggests that the battle of Brunanburh occurred in early October of that year. According to Paul Cavill, the invading armies raided Mercia, from which Æthelstan obtained Saxon troops as he travelled north to meet them. Michael Wood wrote that no source mentions any intrusion into Mercia. According to medieval chroniclers such as John of Worcester and Symeon of Durham, the invaders entered the Humber with a large fleet, although the reliability of these sources is disputed by advocates of an invasion from the west coast of England.