Offa's Dyke

Offa (757 -796 AD) was King of Mercia, a kingdom in what is currently part of England, between the Trent/Mersey rivers in the North to the Thames Valley in the South, and from the Welsh border in the West to the Fens in the East. At the height of his power, however, he also controlled Kent, East Anglia and Lincoln, and had alliances with Northumbria and Wessex. These alliances were sealed by the marriage of two of his daughters to their Kings, Aethelred and Beorhtic respectively. He was, therefore, effectively one of the first Kings of England.