In modern contexts Northumbria usually refers to the region of England between the Tees and Tweed, including to the historic counties of Northumberland and Durham, but may also be taken to be synonymous with North East England. The area corresponds to the rump lands of the historical Kingdom of Northumbria, which later developed into the late medieval county of Northumberland or Comitatus Northumbriae, whose original southern boundary was the River Tees. A representative provincial flag of Northumbria is registered for the area.