Excerpts from Books and Wikipedia
"A stream of restless, landless adventurers from Normandy made their way south to Italy during the eleventh century, looking for the opportunity to carve out a substantial territory for themselves. The most daring and enterprising of these Viking freebooters was Robert Guiscard, the sixth-born of the twelve sons of Tancred of Hauteville. Robert's nickname Guiscard means 'foxlike' or 'wily,' and he proved himself adept in political diplomacy as well as military cunning. In 1059 he made an alliance with the pope, who agreed to recognize Robert as duke of Apulia and Calabria, and the 'future' duke of Sicily, if he could seize and hold these lands for himself, for which he would pay the pope an annual rent of twelve pence per plowland. It took Robert ten years to oust the Byzantines from Calabria, finally driving them from their last foothold in Bari in April 1071. He next focused his attention on Sicily, which was in Arab hands at the time. With his brother Roger, he swiftly crossed the Straits of Messina and laid siege to Palermo, which fell to them in January 1072. . . . Roger's son, Roger II (c.1095-1154), continued with the campaign and later united all the Norman lands in south Italy and Sicily . . ."