Note:  Do not rely on this information. It is very old.

Offa's Dyke

Offa's Dyke, a great entrenchment, 100 miles long, constructed by Offa, King of Mercia, about 780 A.D. Starting at Newmarket, in Flintshire, near the mouth of the river Dee, it traverses the counties of Flint, Denbigh, Salop, Radnor, Hereford, and Monmouth, ending at Beachley, where the Wye joins the Severn.