was in Mercia in fairly recent time a certain vigorous king called Offa, who terrified all the neighbouring kings and provinces around him, and who had a great dyke built between Wales and Mercia from sea to sea". In 1955, Sir Cyril Fox published the first major survey of the Dyke. He concurred with Asser that the earthwork ran 'from sea to sea', theorising that the Dyke ran from the River Dee estuary in the north to the River Wye in the south: approximately . Although Fox observed that Offa's Dyke was not a continuous linear structure, he concluded that earthworks were raised in only those areas where natural barriers did not already exist. Sir Frank Stenton, the UK's most eminent 20th-century scholar on Anglo-Saxon England, accepted Fox's conclusions. He wrote the introduction to Fox's account of the Dyke. Although Fox's work has now been revised to some extent, it still remains a vital record of some stretches of Offa's Dyke that still existed between 1926 and 1928, when his three field surveys took place, but have since been destroyed. Later research In 1978, Dr Frank Noble challenged some of Fox's conclusions, stirring up new academic interest in Offa's Dyke. His MPhil thesis entitled "Offa's Dyke Reviewed" (1978) raised several questions concerning the accepted historiography of Offa's Dyke. Noble postulated that the gaps in the Dyke were not due to the incorporation of natural features as defensive barriers, but instead the gaps were a "ridden boundary", perhaps incorporating palisades, that left no archaeological trace. Noble also helped establish the Offa's Dyke Association, which maintains the Offa's Dyke Path. This long-distance footpath mostly follows the route of the dyke and is a designated British National Trail. John Davies wrote of Fox's study: "In the planning of it, there was a degree of consultation with the kings of Powys and Gwent. On the Long Mountain near Trelystan, the dyke veers to the east, leaving the fertile slopes in the hands of the Welsh; near Rhiwabon, it was designed to ensure that Cadell ap Brochwel retained possession of the Fortress of Penygadden." And, for Gwent, Offa had the dyke built "on the eastern crest of the gorge, clearly with the intention of recognizing that the River Wye and its traffic belonged to the kingdom of Gwent". Ongoing research and archaeology on Offa's Dyke has been undertaken for many years by the Extra-Mural Department