where is northumbria
Northumbria was formed by Ãthelfrith Ã¦thelfrith in Central Great britain In-Anglo saxon. Times at the beginning of the 7th, century the two kingdoms Of bernicia And deira were. (Unified in the 12th century writings Of henry Of huntingdon the kingdom was defined as one of The heptarchy Of-Anglo saxon). kingdomsn the northern border, Berwick-upon-Tweed, which is north of the Tweed but had changed hands many times, was defined as subject to the laws of England by the Wales and Berwick Act 1746. The land once part of Northumbria at its peak is now divided by modern administrative boundaries: 1  North East England.