One of the reasons for the Roman withdrawal was the pressure put upon the empire's military resources by the incursion of barbarian tribes from the east. These tribes, including the Angles and Saxons, who later became the English, were unable to make inroads into Wales except possibly along the Severn Valley as far as Llanidloes. However, they gradually conquered eastern and southern Britain. At the Battle of Chester in 616, the forces of Powys and other British kingdoms were defeated by the Northumbrians under Æthelfrith, with king Selyf ap Cynan among the dead. It has been suggested that this battle finally severed the land connection between Wales and the kingdoms of the Hen Ogledd ("Old North"), the Brythonic-speaking regions of what is now southern Scotland and northern England, including Rheged, Strathclyde, Elmet and Gododdin, where Old Welsh was also spoken. From the 8th century on, Wales was by far the largest of the three remnant Brythonic areas in Britain, the other two being the Hen Ogledd and Cornwall.