Earthwork in western England.
It stretches 169 mi (270 km) from the River Severn near Chepstow to the seaward end of the River Dee's estuary. It was built by Offa of Mercia to fortify the boundary between his kingdom and the lands of the Welsh; for centuries it marked the England-Wales boundary. It consisted of a plain bank (in places some 60 ft [18 m] high) and a ditch (12 ft [3.7 m] deep). Many sections remain, and a walking path now runs its length.