It was not the Roman mission which finally succeeded in converting the North and the Midlands. That success was due to the Scottish and Pictish Church. At the end of the sixth century, Columba, an Irish missionary, crossed over to the solitary rock of Iona, where he established an abbey on the Irish model, and quickly evangelised the northern Picts. From Iona, some generations later, went forth the devoted missionaries who finally converted the northern half of England.
The native churches of the west, cut off from direct intercourse with the main body of Latin Christendom, had retained certain habits which were now regarded by Rome as schismatical. Chief among these were the date of celebrating Easter, and the uncanonical method of cutting the tonsure in a crescent instead of a circle. Augustine, shortly after his arrival, endeavoured to obtain unity between the two churches on these matters of discipline, to which great importance was attached as tests of submission to the Latin rule. He obtained from Æthelberht a safe-conduct through the heathen West-Saxon territories as far as what is now Worcestershire; and there, "on the borders of the Huiccii and the West-Saxons," says Bæda, "he convened to a colloquy the bishops and doctors of the nearest province of the Britons, in the place which, to the present day, is called in the English language, Augustine's Oak." Such open-air meetings by sacred trees or stones were universal in England both before and after its conversion. "He began to admonish them with a brotherly admonition to embrace with him the Catholic faith, and to undertake the common task of evangelising the pagans. For they did not observe Easter at the proper period: moreover, they did many other things contrary to the unity of the Church." But the Welsh were jealous of the intruders, and refused to abandon their old customs. Thereupon, Augustine declared that if they would not help him against the heathen, they would perish by the heathen. A few years later, after Augustine's death, this prediction was verified by Æthelfrith of Northumbria, whose massacre of the monks of Bangor has already been noticed.
It was in return for the destruction of Chester and the slaughter of the monks that Cadwalla joined the heathen Penda against his fellow Christian Eadwine. But the death of Eadwine left the throne open for the house of Æthelfrith, whose place Eadwine had taken. After a year of renewed heathendom, however, during part of which the Welsh Cadwalla reigned over Northumbria, Oswald, son of Æthelfrith, again united Deira and Bernicia under his own rule. Oswald was a Christian, but he had learnt his Christianity from the Scots, amongst whom he had spent his exile, and he favoured the introduction of Pictish and Scottish missionaries into Northumbria. The Italian monks who had accompanied Augustine were men of foreign speech and manners, representatives of an alien civilisation, and they attempted to convert whole kingdoms en bloc by the previous conversion of their rulers. Their method was political and systematic. But the Pictish and Irish preachers were men of more Britannic feelings, and they went to work with true missionary earnestness to convert the half Celtic people of Northumbria, man by man, in their own homes. Aidan, the apostle of the north, carried the Pictish faith into the Lothians and Northumberland. He placed his bishop-stool not far from the royal town of Bamborough, at Lindisfarne, the Holy Island of the Northumbrian coast. Other Celtic missionaries penetrated further south, even into the heathen realm of Penda and his tributary princes. Ceadda or Chad, the patron saint of Lichfield, carried Christianity to the Mercians. Diuma preached to the Middle English of Leicester with much success, Peada, their ealdorman, son of Penda, having himself already embraced the new faith. Penda had slain Oswald in a great battle at Maserfeld in 641; but the martyr only brought increased glory to the Christians: and Oswiu, who succeeded him, after an interval of anarchy, as king of Deira (for Bernicia now chose a king of its own), was also a zealous adherent of the Celtic missionaries. Thus the heterodox Church made rapid strides throughout the whole of the north.
Meanwhile, in the south the Latin missionaries, urged to activity, perhaps, by the Pictish successes, had been making fresh progress. In the very year when Oswald was chosen king by the Northumbrians, Birinus, a priest from northern Italy, went by command of the pope to the West Saxons: and after twelve months he was able to baptise their king, Cynegils, at his capital of Dorchester, on the Thames, his sponsor being Oswald of Northumbria. A year later, Felix, a Burgundian, "preached the faith of Christ to the East Anglians," who had indeed been converted by the Augustinian missionaries, but afterwards relapsed. Only Sussex and Mercia still remained heathen. But, in 655, Penda made a last attempt against Northumbria, which he had harried year after year, and was met by Oswiu at Winwidfield, near Leeds; the Christians were successful, and Penda was slain, together with thirty royal persons—petty princes of the tributary Mercian states, no doubt. His son, Peada, the Christian ealdorman of the Middle English, succeeded him, and the Mercians became Christians of the Pictish or Irish type. "Their first bishop," says Bæda, "was Diuma, who died and was buried among the Middle English. The second was Cellach, who abandoned his bishopric, and returned during his lifetime to Scotland (perhaps Ireland, but more probably the Scottish kingdom in Argyllshire). Both of these were by birth Irishmen. The third was Trumhere, by race an Englishman, but educated and ordained by the Irish." Thus Roman Christianity spread over the whole of England south of the Wash (save only heathen Sussex): while the Irish Church had made its way over all the north, from the Wash to the Firth of Forth. The Roman influence may be partly traced by the Roman alphabet superseding the old English runes. Runic inscriptions are rare in the south, where they were regarded as heathenish relics, and so destroyed: but they are comparatively common in the north. Runics appear on the coins of the first Christian kings of Mercia, Peada and Æthelred, but soon die out under their successors.
Heathendom was now fairly vanquished. It survived only in Sussex, cut off from the rest of England by the forest belt of the Weald. The next trial of strength must clearly lie between Rome and Iona.
The northern bishops and abbots traced their succession, not to Augustine, but to Columba. Cuthberht, the English apostle of the north, who really converted the people of Northumbria, as earlier missionaries had converted its kings, derived his orders from Iona. Rome or Ireland, was now the practical question of the English Church. As might be expected, Rome conquered. To allay the discord, King Oswiu summoned a synod at Streoneshalch (now known by its later Danish name of Whitby) in 664, to settle the vexed question as to the date of Easter. The Irish priests claimed the authority of St. John for their crescent tonsure; the Romans, headed by Wilfrith, a most vigorous priest, appealed to the authority of St. Peter for the canonical circle. "I will never offend the saint who holds the keys of heaven," said Oswiu, with the frank, half-heathendom of a recent convert; and the meeting shortly decided as the king would have it. The Irish party acquiesced or else returned to Scotland; and thenceforth the new English Church remained in close communion with Rome and the Continent. Whatever may be our ecclesiastical judgment of this decision, there can be little doubt that its material effects were most excellent. By bringing England into connection with Rome, it brought her into connection with the centre of all then-existing civilisation, and endowed her with arts and manufactures which she could never otherwise have attained. The connection with Ireland and the north would have been as fatal, from a purely secular point of view, to early English culture as was the later connection with half-barbaric Scandinavia. Rome gave England the Roman letters, arts, and organisation: Ireland could only have given her a more insular form of Celtic civilisation.