The chronicle of Leo Marsicanus recounts the history of the abbey of Montecassino from its foundation by St. Benedict in the sixth-century up to 1075. It presents a detailed and compelling story of tribulation and renewal, with the abbey twice destroyed and abandoned in the early Middle Ages and then rebuilt. It concludes with an informative account of the building and dedication of the new abbey church by Abbot Desiderius in 1066-71. The chronicle is also a key source for the more general history of southern Italy in the early Middle Ages, and of the conquest of the region by the Normans during the eleventh century. In addition, Montecassino was one of the great intellectual centres of western Christendom and a major contributor to the reform movement within the Church during the later eleventh century. Leo’s chronicle is a crucial witness to that role.