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, mostly the Irish (at least 27 times), the Vikings (at least 7 times) and 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 reputedly murdered in a Viking raid in 1106.