But Beomrsed was at once either slain by Offa or driven into exile by the people, and before the year closed Offa succeeded to the Mercian kingship (Flor. Wig. i. 56; Will. Malm. Cfesta Regum, i. 79 ; Chronica Majora, i. 342). Internal troubles had greatly weakened the power of Mercia since the period of Æthelbald's supremacy south of the Humber, which had been lost through his defeat by the West-Saxons at Burford in 754. Wessex had firmly established its independence, and the East-Angles, East-Saxons, and Kentish men were no longer subject to the Mercian king, while it is evident that the Welsh had grown formidable on his western frontier (Green). For fourteen yean after his accession nothing is known of Offa's doings ; those years were apparently epent in making good his position and reducing his kingdom to order. At the end of that time, in 771, he began a career of conquest by the forcible subjugation of the Hestingi (Symbon Historia Regum, ap. 0pp. i. 44). Who these people were is not known ; it is suggested that they were the East-Angles (the two names might easily be confused by a copyist) (Stubbs), and on the other hand that they were a people who have given their name to the town of Hastings (Stmbon, u.s. n.) On the latter assumption Offa's campaign implies a triumphant march through the territory of the East-Saxons, and would have to be reckoned as an early attempt at the conquest of Kent. It is with that kingdom that Offa is next found at war; he defeated the Kentish army in 776 at Otford, and his victory seems to have made Kent subject to him. At this time, too, the East-Saxons were no doubt brought under his supremacy, and their subjection would imply that he gained London, where he is said, though on no good authority, to have built himself a residence. Having brought the south-eastern part of England under his dominion, he made war on the West-Saxons, and in 779 fought with their king, Cynewulf [q. v.], at Bensington, or Benson, in Oxfordshire, and took the town (Anglo-Saxon Chronicle, an. 777). This victory gave him Oxford and the territory north of the Thames that had been lost to Mercia by the battle of Burford, and south of the Thames the country between the Thames and the Berkshire hills as far west as Ashbury (Historia de Abingdon, i. 14 ; Parker, Early Hiftory of Oxford, p. 109). Offa next attacked the Welsh, and under him the English for the first time obtained a permanent increase of territory west of the Severn. In the same year as that of his victory at Bensington he began a series of incursions across the river, and finally, in order to check the retaliatory raids of the Welsh, defined and defended his frontier by an earthwork drawn from the mouth of the Wye to the mouth of the Dee. Offa's dyke, as this earthwork is called, is, roughly speaking and reckoning Monmouthshire as Welsh, still the boundary between England and Wales, though the traces now left of it are few. Offa thus added to Mercia a large part of Powys, together with the town of Pengwern, the modern Shrewsbury (Rhys, Celtic Britain, p. 141 ; Annales Uambrenses, ann. 778-784 ; Asser, ap. Monumenta Historica Britannica, p. 471). The native population remained in the conquered land, and lived side by side with their conquerors. An opportunity of establishing amicable relations with the West-Saxon kingdom occurred on the accession of Beorhtric or Brihtric [q. v.], when Egbert or Ecgberht {d. 839) [q. v.], afterwards king of the West-Saxons, a member of the royal line who had claims to the throne, fled for shelter to the Mercian court. Beorhtric desired that he should be expelled, and in 789 Offa gave Beorhtric his daughter Eadburga or Eadburh [q. v.] in marriage, and drove Egbert from his kingdom.
The commanding position that Offa obtained south of the Humber was recognised on the continent, for Pope Hadrian I, writing to the Frankish king Charles, or Charlemagne, described him as king of the English nation, spoke of a baseless rumour that Offa had proposed to Charles that they should depose the pope, and declared that he had received ambassadors from him with pleasure (Monumenta Carolina, pp. 279-282). Offa soon had need of the pope's assistance in a scheme for the consolidation of the Mercian power. His conquests tended to impress on England a threefold political division into Northumbria, Mercia, and Wessex, and he desired to complete the independent organisation of his kingdom by the institution of a third and Mercian archbishopric, to the prejudice of the rights of the see of Canterbury ; while it can scarcely be doubted that he saw that to weaken Canterbury would strengthen the hold of Mercia upon Kent. His plan was rendered possible by the fact that the conquest of Kent had made Archbishop Jaenbert [q. v.] his subject. In accordance with his request the pope sent to England two legates named George and Theophylact, who, in a synod held at Celchyth, or Chelsea, in 787, sanctioned the surrender by Jaenbert of his rights over the sees of Worcester, Leicester, Lindsay, Elmham, and Dunwich, in order to form an archbishopric for the see of Lichfield, then held by Higbert [q. v.] This arrangement received the papal approval, and
