Offa's Dyke

Coordinates: 52°20′38″N 3°02′56″W / 52.344°N 3.049°W / 52.344; -3.049

Offa's Dyke (Welsh: Clawdd Offa) is a large linear earthwork that roughly follows the current border between England and Wales. The structure is named after Offa, the 8th century king of Mercia, who is traditionally believed to have ordered its construction. Although its precise original purpose is debated, it delineated the border between Anglian Mercia and the Welsh kingdom of Powys.

The Dyke, which was up to 65 feet (20 m) wide (including its flanking ditch) and 8 feet (2.4 m) high, traversed low ground, hills and rivers. Today the earthwork is protected as a scheduled monument. Some of its route is followed by the Offa's Dyke Path; a 176 mi (283 km) long-distance footpath that runs between Liverpool Bay in the north and the Severn Estuary in the south.

Although the Dyke is conventionally dated to the Early Middle Ages of Anglo-Saxon England, research in recent decades - using techniques such as radioactive carbon dating - has challenged the conventional historiography and theories about the earthwork.