Query: Geographically, what river was Northumbria north of?
Context: Mercian and Northumbrian are together referred to as Anglian. In terms of geography the Northumbrian region lay north of the Humber River; the Mercian lay north of the Thames and South of the Humber River; West Saxon lay south and southwest of the Thames; and the smallest, Kentish region lay southeast of the Thames, a small corner of England. The Kentish region, settled by the Jutes from Jutland, has the scantiest literary remains.