One of the most important kingdoms of Anglo-Saxon England, lying north of the Humber River. During its peak period it extended from the Irish Sea to the North Sea, between two west-east lines formed in the north by the Ayrshire coast and the Firth of Forth and in the south by the Ribble/Mersey River and the Humber. It resulted from the union of Deira, with its capital at York, and Bernicia, based on Bamburgh, under Edwin in 622 AD. After the conversion of King Edwin in 626 and the establishment of many major monasteries within the region, Northumbria became a center of missionary activity and a leading center of missionary activity and a leading center for the production of Christian art. In the later 7th-8th centuries, despite political decline, it was the scene of a cultural renaissance, attested by the history of Bede, the illuminated manuscripts of Lindisfarne, etc. Schools of art and monumental architecture also flourished. Archaeologically its most important site is Yeavering, a series of palaces built by Edwin and his successors in northern Northumberland. The cultural life and the political unity of Northumbria were destroyed by the arrival of the Danes.