No part of Europe suffered as much from the fall of the Roman Empire to the barbarian invasions as did Britain. After the last legion pulled out in 410, the island was left to its own resources which proved insufficient to repel the waves of Picts, Saxons, Irish, Angles and Jutes that assailed the Romano-Britons. Civilization gradually died; literacy almost vanished; the barter system replaced coinage; and Christianity retreated into the Welsh hills and the remoter regions; Germanic petty kingdoms were established on the ruins.
The task of reintroducing Christianity fell to Irish monks who evangelized the north and to a mission sent out from Rome in the 590s. Aethelbert, a barbarian king in Kent, had married a Frankish princess who had won permission to include Christian priests in her retinue. Pope Gregory the Great took the opportunity to send monks from his own monastery to the Kentish capital at Canterbury and the expedition was to be led by the abbot Augustine. On the way to his post Augustine apparently heard stories of the bloodthirsty people to whom he was being sent and wanted to turn back. His spine was stiffened by exhortations from Gregory so the monk continued to Britain, arriving in 597.
Augustine’s mission was made easier by a change in Church attitudes to pagan customs. Hitherto, the Church had resolutely resisted the pressures of local culture on the Christian message. Early believers had spent centuries refusing to take part in Roman civic religion, the sacrifices, holiday celebrations, and the bloody arena sports, and suffered for it. But by the start of the 7th century, the papacy was willing to become more accommodating in order to meet the challenge of evangelizing the Germanic barbarians. Pope Gregory sent the following message to Augustine:
By no means destroy the temples of the gods but rather the idols within those temples. Let him, after he has purified them with holy water, place altars and relics of the saints in them. For, if those temples are well built, they should be converted from the worship of demons to the service of the true God. Thus, seeing that their places of worship are not destroyed, the people will banish error from their hearts and come to places familiar and dear to them in acknowledgement and worship of the true God. Further, since it has been their custom to slaughter oxen in sacrifice, they should receive some solemnity in exchange. Let them therefore, on the day of the dedication of their churches, or on the feast of the martyrs whose relics are preserved in them, build themselves huts around their one-time temples and celebrate the occasion with religious feasting. They will sacrifice and eat the animals not any more as an offering to the devil, but for the glory of God to whom, as the giver of all things, they will give thanks for having been satiated. Thus, if they are not deprived of all exterior joys, they will more easily taste the interior ones. For surely it is impossible to efface all at once everything from their strong minds, just as, when one wishes to reach the top of a mountain, he must climb by stages and step by step, not by leaps and bounds.
This policy helped ensure Christmas celebrations over the ages would be syncretic, varied with many local flavours. Moreover, Christmas Day was the date in 597 when Augustine was able to baptize Aethelbert and thousands of his Saxon followers.