to Adomnán of Iona, who referenced the testimony of earlier abbots of Iona who had known Columba, St Columba visited the monastery at Clonmacnoise during the time when he was founding the monastery at Durrow. While he was there he prophesied about the future debates in the churches of Ireland about the dating of Easter and claimed that angels had visited the monastery at Clonmacnoise. While he was there, a young monk named Ernéne mac Craséni (who would later be famous in Ireland) tried to touch Columba's clothes while Columba was not looking. However, the saint immediately noticed and grabbed the boy by the neck, told him to open his mouth, and then blessed him, saying that he would teach the doctrine of salvation. Towards the close of the seventh century a plague carried off a large number of its students and professors. Clonmacnoise's period of greatest growth came between the 8th and 12th centuries. It was attacked frequently during these four centuries, most often by the Irish (at least 27 times), the Vikings (at least 7 times) and the Normans (at least 6 times). The early wooden buildings began to be replaced by more durable stone structures in the 9th century, and the original population of fewer than ten men grew to perhaps 1,500 to 2,000 by the 11th century. Although the site was based around a core of churches, crosses, graves and ecclesiastical dwellings and workshops, it would have been surrounded by the houses and streets of a larger secular community, the metalworkers, craftsmen and farmers who supported the monastic clergy and their students. Artisans associated with the site created some of the most beautiful and enduring artworks in metal and stone ever seen in Ireland, with the Clonmacnoise Crozier (on display in the National Museum of Ireland) and the Cross of the Scriptures representing the apex of their efforts. The Book of the Dun Cow, a vellum manuscript dating to the 12th century, was written here and its main compiler, Máel Muire mac Céilechair meic Cuinn na mBocht was reputedly murdered in a Viking raid in 1106. By the 12th century Clonmacnoise began to decline. The reasons were varied, although attacks by the Vikings (under Turgesius) and the Normans contributed. Without doubt the most debilitating factor was the growth of the town of Athlone to the north of the site from the late-12th century. Athlone became the