Offa's Dyke

Defensive earthwork dyke along the English-Welsh border, of which there are remains from the mouth of the River Dee to that of the River Severn. It was built about AD 785 by King Offa of Mercia, England, and represents the boundary secured by his wars with Wales.

The dyke covered a distance of 240 km/149 mi, of which 130 km/81 mi are still standing. It consists of a large rampart and ditch, the latter usually on the Welsh side, and was laid out to take advantage of natural physical features.