gone into building the dyke are impressive, and suggest that the king who had it built (whether Offa or someone else) had considerable resources at his disposal. Other substantial construction projects of a similar date do exist, however, such as Wat's Dyke and Danevirke, in what is now Germany as well as such sites as Stonehenge from millennia earlier. The dyke can be regarded in the light of these counterparts as the largest and most recent great construction of the preliterate inhabitants of Britain. Church Offa ruled as a Christian king, but despite being praised by Charlemagne's advisor, Alcuin, for his piety and efforts to "instruct [his people] in the precepts of God", he came into conflict with Jænberht, the Archbishop of Canterbury. Jænberht had been a supporter of Ecgberht II of Kent, which may have led to conflict in the 760s when Offa is known to have intervened in Kent. Offa rescinded grants made to Canterbury by Egbert, and it is also known that Jænberht claimed the monastery of Cookham, which was in Offa's possession. In 786 Pope Adrian I sent papal legates to England to assess the state of the church and provide canons (ecclesiastical decrees) for the guidance of the English kings, nobles and clergy. This was the first papal mission to England since Augustine had been sent by Pope Gregory the Great in 597 to convert the Anglo-Saxons. The legates were Bishop George of Ostia, and Theophylact, the bishop of Todi. They visited Canterbury first, and then were received by Offa at his court. Both Offa and Cynewulf, king of the West Saxons, attended a council where the goals of the mission were discussed. George then went to Northumbria, while Theophylact visited Mercia and "parts of Britain". A report on the mission, sent by the legates to Pope Adrian, gives details of a council held by George in Northumbria, and the canons issued there, but little detail survives of Theophylact's mission. After the northern council George returned to the south and another council was held, attended by both Offa and Jænberht, at which further canons were issued. In 787, Offa succeeded in reducing the power of Canterbury through the establishment of a rival archdiocese at Lichfield. The issue must have been discussed with the papal legates in 786, although it is not mentioned in the accounts that have survived. The Anglo-Saxon Chronicle reports a "contentious synod"