Offa's Dyke

Great English earthwork extending linearly, with some gaps, from the River Severn near Chepstow to the seaward end of the Dee estuary, passing for 169 miles (270 kilometres) through the counties of Gloucestershire, Herefordshire, Radnorshire, Montgomeryshire, Shropshire, Denbighshire, and Flintshire. It was built at the orders of Offa, the great Mercian king of the second