The Sack of Rome in the year 410 prompted a complete Roman departure from Britain, and Cornwall then experienced an influx of Celtic Christian missionaries from Ireland who had a profound effect upon the early Cornish people, their culture, faith and architecture. The ensuing decline of the Roman Empire encouraged the Anglo-Saxon invasion of Britain. The Angles, Jutes, Frisii and Saxons, Germanic peoples from northern Europe, established petty kingdoms and settled in different regions of what was to become England, and parts of southern Scotland, progressively defeating the Britons in battle. The Saxons of the Kingdom of Wessex in particular were expanding their territory westwards towards Cornwall. The Cornish were frequently embattled with the West Saxons, who used their Germanic word "walha" (modern English: Welsh) meaning "stranger" or "foreigner", to describe their opponents, later specifying them as the "Westwalas" (West Welsh) or "Cornwalas" (the Cornish). Conflict continued until King Athelstan of England determined that the River Tamar be the formal boundary between the West Saxons and the Cornish in the year 936, making Cornwall one of the last retreats of the Britons encouraging the development of a distinct Cornish identity; Brittonic culture in Britain became confined to Cornwall, parts of Devon, North West England, South West Scotland and Wales. Although a treaty was agreed, Anglo-Saxon political influence stretched westwards until some time in the late 10th century when "Cornwall was definitively incorporated into the Kingdom of England".