Offa was King of Mercia from 757 to 796 AD. His kingdom covered the area between the Trent/Mersey rivers in the North to the Thames Valley in the South, and from the Welsh border in the West to the Fens in the East. At the height of his power, however, he also controlled Kent, East Anglia and Lindsay (Lincoln), and had alliances with Northumbria and Wessex, sealed by the marriage of two of his daughters to their Kings, Aethelred and Beorhtic respectively. He was, therefore, effectively an early King of England. He influenced the setting up of a third Archbishopric in England at the Cathedral at Lichfield and near his principal residence at Tamworth. This, however, was abolished shortly after his death.
Offa was also influential in international affairs, having diplomatic and trading links with Charlemagne the poweful continental king based in Francia, together with contact with the Papacy. He established the use of the penny as the standard monetary unit in England, with the same silver content as coins in circulation in Francia, thereby assisting both national and international trading.
Offa’s Dyke is a linear earthwork which roughly follows the Welsh/English boundary. It consists of a ditch and rampart constructed with the ditch on the Welsh-facing side, and appears to have been carefully aligned to present an open view into Wales from along its length. As originally constructed, it must have been about 27 metres wide and 8 metres from the ditch bottom to the bank top.
The origins of the Dyke are shrouded in mystery so that many of its aspects are speculated upon rather than being fully understood. Asser, the biographer of King Alfred, gave the first known reference to it when he wrote, about 100 years later that a certain vigorous king called Offa……had a great dyke built between Wales and Mercia from sea to sea.
The Dyke appears to have been constructed in response to events in the border region involving the Princes of Powys, but whether it was intended as an agreed boundary, as a defensive structure with long lost additional fortifications, or for some other use, is not known. It is thought to have been started in about 785 AD and to have taken several years to build. The 9th Century history of the region suggests that the earthwork had only a short period of importance and was then abandoned.
Much of the Dyke is still traceable along the 80 miles from the Wye valley to Wrexham. In places it still retains most of its original impressive dimensions while in other parts it has disappeared due to 1200 years of farming activity and its presence can only be detected by archaelogical work. Two stretches of earthwork at each end of this length are not now considered to be the work of Offa’s time, but the King filling much of the central section gave Asser the licence to describe the Dyke as going from sea to sea.
Historical research and archaeology on Offa’s Dyke has been undertaken for many years by the Extra-Mural department of the University of Manchester. The Porth y Waen Study Centre, near Oswestry, gives the public an opportunity to take part in such work. Details of the wide range of courses available for both novice and expert historians and archaeologists can be obtained from the Centre on telephone number +44 (0) 1691 828900.