traditions of the Celtic church in favour of Roman practices. When he returned to England, he became abbot of a new monastery at Ripon in 660. Wilfrid advocated acceptance of the authority of Rome at the Synod of Whitby. The two-halves of the double monastery Monkwearmouth–Jarrow were founded by the nobleman Benedict Biscop in 673 and 681. Biscop became the first abbot of the monastery, and travelled to Rome six times to buy books for the library. His successor, Abbot Ceolfrith, continued to add to the library until by one estimate the library at Monkwearmouth–Jarrow had over two hundred volumes. One who benefited from this library was Bede. In the early seventh century in York, Paulinus founded a school and a minster, but not a monastery. The School at York Minster is one of the oldest in England. By the late eighth century, the school had a noteworthy library, estimated at one hundred volumes. Alcuin was a student and teacher at York before he left for the court of Charlemagne in 782. Synod of Whitby In 664, King Oswiu called the Synod of Whitby to determine whether to follow Roman or Irish customs. Since Northumbria was converted to Christianity by the Celtic clergy, the Celtic tradition for determining the date of Easter and Irish tonsure were supported by many, particularly by the Abbey of Lindisfarne. Roman Christianity was also represented in Northumbria, by Wilfrid, Abbot of Ripon. By the year 620, both sides were associating the other's Easter observance with the Pelagian Heresy. The King decided at Whitby that Roman practice would be adopted throughout Northumbria, thereby bringing Northumbria in line with Southern England and Western Europe. Members of the clergy who refused to conform, including the Celtic Bishop Colman of Lindisfarne, returned to Iona. The episcopal seat of Northumbria transferred from Lindisfarne to York, which later became an archbishopric in 735. Impact of Scandinavian raiding, settlement and culture The Viking attack on Lindisfarne in 793 was the first of many raids on monasteries of Northumbria. The Lindisfarne Gospels survived, but monastic culture in Northumbria went into a period of decline in the early ninth century. Repeated Viking assaults on religious centres were one reason for the decrease in production of manuscripts and communal monastic culture. After 867, Northumbria came under control of the Scandinavian forces, and there was an influx of Scandinavian immigrants. Their religion was pagan and had