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 AEthelfrith, 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 AEthelfrith, 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.