Offa's Dyke

Offa's Dyke (Welsh: Clawdd Offa) is a large linear earthwork that roughly follows the border between England and Wales. The structure is named after Offa, the Anglo-Saxon king of Mercia from 757 to 796, who is traditionally believed to have ordered its construction, although modern archaeological evidence shows far earlier origins and its original purpose is debated. It delineated the border between Anglian Mercia and the Welsh kingdoms (such as Powys) by the time of its completion, but when begun (carbon-dated to 430AD) it separated the Brytons of the Decangi, Cornovi and Dobunni from the Western Ordovices, Demetae and Silures. The earthwork, 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, it is protected as a scheduled monument. Some of its route is followed by the Offa's Dyke Path, a 177-mile (285 km) long-distance footpath that runs between Liverpool Bay in the north and the Severn Estuary in the south. Although the dyke has conventionally been dated to the Early Middle Ages of Anglo-Saxon England, research in recent decades—using techniques such as radiocarbon dating—has challenged the conventional historiography and theories about the earthwork and showed that construction was started in the early 5th century, during the sub-Roman period.