Offa's Dyke is a massive earthwork between England and Wales, running from the estuary of the River Dee in the north to the River Wye in the south (approximately 240 km). The dyke is not continuous, being built only in areas where natural barriers did not already exist, so its total length is only 130 km. In places, it is up to 20 m wide (including its surrounding ditch) and 2.5m high.

The earthwork is widely attributed to Offa, King of Mercia in the 8th century. It is not known to what extent Offa was indeed responsible for building the dyke - important parts of it may date from earlier periods.

The barrier may have been planned as a limited defensive measure against the depredations of the Welsh, but its major use seems to have been as a boundary between England and Wales.

"[I]t was customary for the English to cut off the ears of every Welshman who was found to the east of the dyke, and for the Welsh to hang every Englishman whom they found to the west of it"

George Borrow, Wild Wales [from folklore]

Today, the England-Wales border still mostly follows the dyke. It has a cultural significance symbolising the separation between the two countries similar to the symbolism of Hadrian's Wall between England and Scotland.

Offa's Dyke Path, a footpath which mostly follows the route of the dyke, is one of the designated British National Trails.

See also

• Götavirke (Geatish Dyke)
• Danevirke (Danish Dyke)