Offa's Dyke () 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 AD 757 until 796, 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 earthwork, which was up to wide (including its flanking ditch) and 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 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 radioactive carbon dating – has challenged the conventional historiography and theories about the earthwork and shows that part was started in the early 5th century, during the sub-Roman period. History Background The generally accepted theory of the earthwork attributes most of its construction to Offa, King of Mercia from 757 to 796. The structure did not represent a mutually agreed boundary between the Mercians and the Kingdom of Powys. It had a ditch on the Welsh (western) side, with the displaced soil piled into a bank on the Mercian (eastern) side. This suggests that Mercians constructed it as a defensive earthwork, or to demonstrate the power and intent of their kingdom. Throughout its entire length, the Dyke provides an uninterrupted view from Mercia into Wales. Where the earthwork encounters hills or high ground, it passes to the west of them. Although historians often overlook Offa's reign because of limitations in source material, he ranks as one of the greatest Anglo-Saxon rulers – as evidenced in his ability to raise the workforce and resources required to construct Offa's Dyke. The construction of the earthwork probably involved a corvée system requiring vassals to build certain lengths of the earthwork for Offa in addition to performing their normal services to their king. The Tribal Hidage, a primary document, shows the distribution of land within 8th-century Britain; it shows that peoples were located within specified territories for administration. Early scholarship The first historians and archaeologists to examine the Dyke seriously compared their conclusions with the late 9th-century writer Asser, who wrote: "there