battle of Heathfield, and united under his power those who were properly called Mercians and the other English tribes south of the Humber. He also conquered the West Saxon districts along the Severn, and thus established what is generally known as the Kingdom of Mercia. Paulinus had fled from York after the battle of Heathfield. But the contest between heathen and Christian was renewed by Oswald, Eadwine’s successor; for Paulinus’ place was taken by Bishop Aidan, a missionary from Columba’s Irish monastery in Iona, who had established an Episcopal See in the Island of Lindisfarne. From thence missionaries issued, who continued the work of conversion, to which Oswald chiefly devoted his life. Birinus, sent from Rome, with the support of Oswald, succeeded in converting even Wessex, and establishing a Christian church at Dorchester. Penda still continued in the centre of England to uphold the cause of heathendom. At the battle of Maserfield he conquered and slew Oswald, and re-established his religion for a time in Wessex. But at length, in 655, he succumbed to Oswi, Oswald’s successor, and with him fell the power of heathendom. It seemed as though Irish Christianity, and not Roman, would thus be the religion of England. But Rome did not suffer her conquests to slip from her hand. A struggle arose between the adherents of the two Churches. The matter was brought to an issue in 664 at a Council at Whitby. The Roman Church there proved predominant. And this victory was followed by the appointment of Theodore of Tarsus, an Eastern divine, to the See of Canterbury. Under him the English Church was organized. Fresh sees were added to the old ones, which had usually followed the limits of the old English kingdoms. Canterbury was established as the centre of Church authority. Theodore’s ecclesiastical work tended much both to the growth of national unity and to the close connection of Church and State which existed during the Saxon period. The unity of the people was expressed in the single archiepiscopal See of Canterbury and in the Synods; while the arrangement of bishoprics and parishes according to existing territorial divisions connected them closely with the State. [Sidenote: Supremacy of Mercia. 716-819.] The contest for supremacy between Mercia and Northumbria still continued. After the fall of Penda, the supremacy of the Northern kingdom was for some time unquestioned. But sixty years later, during the reign of three Christian kings, Ethelbald, Offa, and Cenwulf (716-819), Mercia again rose to great power. Offa indeed came nearer to consolidating an empire than any of the preceding kings, although he is not mentioned among the Bretwaldas. It is said that he corresponded on terms of something like equality with Charlemagne; and the great dyke between the Severn and the Wye which bears his name is supposed to mark the limits of his conquests over the Britons. [Sidenote: Ecgberht. 800-836.] [Sidenote: Consolidation under the West Saxons.]