In the latter half of the eighth century Offa, king of Mercia, was the most powerful monarch in England, and, among other conquests, subdued Kent and added it to his dominions. The course of political events tended to a threefold division of England into the Northumbrian, Mercian, and West Saxon kingdoms, and the twofold system of ecclesiastical administration by the metropolitans of Canterbury and York thwarted the ambition of the Mercian king. Northumbria had already sealed its policy of separation by the restoration of the archbishopric of York, and Offa now adopted a similar course, by persuading Pope Hadrian I. to grant the see of Lichfield metropolitan dignity. He had a special reason for weakening the power of Canterbury, for after the extinction of Kentish royalty the archbishop gained increased political importance, and became the representative of the national life of the kingdom, which Offa vainly endeavoured to crush. Accordingly two legates of Hadrian held a synod at Chelsea in 787, in which Higberht, bishop of Lichfield, was declared an archbishop. Jaenberht, archbishop of Canterbury, was forced to submit to the partition of his province, the obedience of the Mercian and East Anglian bishops being apparently transferred to the new metropolitan. This arrangement was subversive of a part of Theodore's work that was specially valuable as regards the development both of the Church and the nation. Theodore had made ecclesiastical jurisdictions independent of the fluctuations of political boundaries, and had freed the Church from provincial influences and from a merely local character. The national character of the Church was to become a powerful factor in forming the English nation. In spite of civil divisions, the oneness of the Church was a strong element of union. Although no lay assembly, no witenagemot, of the whole nation was as yet possible, the Church met in national councils; its head, the archbishop of Canterbury, might be a native of any kingdom, and every one of its clergy, of whatever race he might be, was equally at home in whatever part of the land he was called to minister. This national character of the Church and the influence it exercised on national unity were endangered by creating metropolitan jurisdiction and dignity as mere appendages to a political division. Happily there was no second archbishop of Lichfield. Offa's successor, Cenwulf, found AEthelheard, the archbishop of Canterbury, a useful ally in a revolt of the Kentish nobles, and joined him in obtaining the restoration of the rights of his see from Leo III. While the see of York was overwhelmed by political disasters, the archbishop of Canterbury gained increased importance. Wessex entered on a career of conquest under Ecgberht, who, in 827, defeated the Mercian king at Ellandun. This victory led to the conquest of Kent, and in 838 Archbishop Ceolnoth, in a council held at Kingston, made a treaty of