At the beginning of the eleventh century the tide of Saracen invasion was at its height, and it seemed as though the Tyrrhenian Sea, nay, even the Mediterranean itself, was destined to be converted into a Moslem lake. Before its close the Communes of Pisa and Genoa had freed their sea from foreign invaders. Thereafter, they swept the coasts of Africa, and, sword in hand, imposed commercial treaties upon their old antagonists. The conquest of Sicily by the Normans and the victories of the Venetians in the Adriatic, with the consequent acquisition of trading privileges in the Levant, were contemporaneous with these achievements, and all of them prolegomenal to the Crusades.

Already, in the tenth century, the Pisans had fought the Saracens in Calabria, and, perhaps, also in Spain and Africa; while, in 1004, a Moslem fleet sailed up the Arno and sacked a quarter of the city. To avenge this insult and to defend their commerce, the Pisans attacked Reggio. No trustworthy details of the expedition have come down to us, though, according to a comparatively modern legend, it was undertaken at the instance of the learned French monk, Gerbert of Aurillac, who, after he had ascended the Papal throne with the title of Sylvester II, proclaimed a crusade for the deliverance of Jerusalem. On his invitation, the Pisans put to sea and assailed and slaughtered the first infidels they encountered.