added by archaeologs A linear earthwork, 192 km long, built by King Offa of Mercia (r. 757-96) as a frontier between his kingdom and the kingdom of Powys. It consists of a large earthen bank and quarry ditch, and runs almost continuously between Treuddy and Chepstow, close to the border of England and Wales. Archaeologists, among them Sir Cyril Fox, have tried to locate secondary timber fortifications on its length, so far without success. Offa’s reign is also noteworthy for the close connections he established between Mercia and the Carolingian empire — he married his daughter to one of Charlemagne’S sons — and the introduction of regular coinage based on pennies.
The Macmillan dictionary of archaeology, Ruth D. Whitehouse, 1983