Offa (d. 796), king of Mercia, obtained that kingdom in A.D. 757, after driving out Beornred, who had succeeded a few months earlier on the murder of A z Ethelbald. He traced his descent from Pybba, the father of Penda, through Eowa, brother of that king, his own father's name being Thingferth. In 779 he was at war with Cynewulf of Wessex from whom he wrested Bensington. It is not unlikely that the Thames became the boundary of the two kingdoms about this time. In 787 the power of Offa was displayed in a synod held at a place called Cealchyth. He deprived Taenberht, archbishop of Canterbury, of several of his suffragan sees, and assigned them to Lichfield, which, with the leave of the pope, he constituted as a separate archbishopric under Hygeberht. He also took advantage of this meeting to have his son Ecgferth consecrated as his colleague, and that prince subsequently signed charters as Rex Merciorum. In 789 Offa secured the alliance of Berhtric of Wessex by giving him his daughter Eadburg in marriage. In 794 he appears to have caused the death of ZEthelberht of East Anglia, though some accounts ascribe the murder to Cynethryth, the wife of Offa. In 796 Offa died after a reign of thirty-nine years and was succeeded by his son Ecgferth. It is customary to ascribe to Offa a policy of limited scope, namely the establishment of Mercia in a position equal to that of Wessex and of Northumbria. This is supposed to be illustrated by his measures with regard to the see of Lichfield. It cannot be doubted, however, that at this time Mercia was a much more formidable power than Wessex. Offa, like most of his predecessors, probably held a kind of supremacy over all kingdoms south of the Humber. He seems, however, not to have been contented with this position, and to have entertained the design of putting an end to the dependent kingdoms. At all events we hear of no kings of the Hwicce after about 780, and the kings of Sussex seem to have given up the royal title about the same time. Further, there is no evidence for any kings in Kent from 784 until after Offa's death. To Offa is ascribed by Asser, in his life of Alfred, the great fortifications against the Welsh which is still known as "Offa's dike." It stretched from sea to sea and consisted of a wall and a rampart. An account of his Welsh campaigns is given in the Vitae duorum Off arum, but it is difficult to determine how far the stories there given have an historical basis.
See Anglo-Saxon Chronicle, ed. J. Earle and C. Plummer (Oxford, 18 99), s.a. 755, 777, 7 8 5, 7 8 7, 79 2, 794, 79 6, 836; W. de G. Birch, Cartularium Saxonicum (London, 1885-1893), vol. i.; Asser, Life of Alfred, ed. W. H. Stevenson (Oxford, 1904) Vitae duorum Offarum (in works of Matthew Paris, ed. W. Wats, London, 1640).
