Collier's New Encyclopedia (1921)/Offa's Dyke
OFFA'S DYKE, an entrenchment extending along the border of England and Wales, from the N. coast of Flintshire, on the estuary of the Dee, through Denbigh, Montgomery, Salop, Radnor, and Hereford, into Gloucestershire, where its S. termination is near the mouth of the Wye. In some places it is nearly obliterated by cultivation; in others it is of considerable height. Nearly parallel with it, about 2 miles to the E., is Watt's Dyke, which, however, seems never to have been so great a work. Offa, King of Mercia, is said to have erected Watt's Dyke in 765 to keep back the Welsh, and Offa's Dyke a few years later.