In the early 1200s the chronicler Ibn al-Athir, surveying the events of the past century, stated that the Norman conquest of southern Italy was part of a coordinated counter-offensive against Islam. In al-Athir's telling, what became the First Crusade was initially meant to help Roger of Sicily pursue further conquests, preferably an invasion of Ifriqiya, modern-day Tunisia. But Roger found that plan ridiculous, supposedly indicating his opinion through loud flatulence. “If you are determined to wage holy war on the Muslims,” he said, “then the best way is to conquer Jerusalem. You will free it from their hands and have glory.” The genesis of the First Crusade, in this telling, lay in the Norman conquest of Sicily and southern Italy. Whether this anecdote has any grounding in historical reality or not, it represents a widely held belief, dating to the medieval period, that the Norman conquest of southern Italy was integral to the First Crusade. Whether in terms of military strategy, personnel, geopolitical objectives, the movement of peoples, or the ideology of holy war, the activities of the Normans in Italy between 1000 and 1091 and in the eastern Mediterranean between 1196 and 1119 are assumed to have some kind of connection.

Historians have long puzzled over these issues, and their answers have reflected the state of the scholarship at any given moment. Generations of historians, such as David Douglas and Matthew Bennett, have tended to see the southern Norman contingents of the First Crusade as part of a larger “Normanitas” that sought to conquer the world, or large parts of it. Charles Homer Haskins, surveying the history of the Normans of the South, stated that their story “would be conclusive proof of the creative power of the Norman genius for conquest and administration”. Other specialists such as Graham Loud, Elisabeth Van Houts, David Bates, and Kenneth Baxter Wolf have de-emphasised such abstract organising principles and, instead, focused on the evolving and complex relationship of the southern Normans with the Reform movement in the Catholic Church and Normans’ own sense of identity.