Offa (757 -796 AD) was King of Mercia, a kingdom in what is currently part of England, 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 Lincoln, and had alliances with Northumbria and Wessex. These alliances were sealed by the marriage of two of his daughters to their Kings, Aethelred and Beorhtic respectively. He was, therefore, effectively one of the first Kings of England.
Within two miles, there is a famous thing; Cai'de Offa's Dyke, that reacheth farre in length;
Offa's Dyke inspires thousands of tourists and walkers, wishing to walk the official Trail, which was opened in 1971, thanks mainly to the efforts of volunteers from the Offa's Dyke Association. The Trail is maintained by local authorities coordinated by the Countryside Council for Wales (including the sections in England), and the Ramblers' Association remains active in maintaining and promoting the route and running the Offa's Dyke Information Centre 
- Thomas Churchyard, The Worthines of Wales', 1587, see: http://www.wansdyke21.org.uk/wansdyke/wanart/nurse1.htm for a full reference
- see the official National Trail Website: http://www.nationaltrail.co.uk/OffasDyke/
- see the Ramblers association entry on the dyke: http://www.ramblers.org.uk/info/paths/offasdyke.html