in the middle ages the tides of the humber kept armies from crossing. at that time it was thought to be an arm of the ocean. during the anglo-saxon period, the humber was a major boundary, separating northumbria from the southern kingdoms. the name northumbria came from old english "northanhymbre" meaning "the people north of the humber". the vikings used the humber and its two tributaries, the ouse and trent, with their shallow-draft longships to raid all over northeastern england.