When English-speaking historians mention the Norman Conquest, they are usually referring to the invasion of England in 1066 by Normans under the leadership of William the Conqueror. The first Norman Conquest, however, came in Sicily six years before the more famous invasion of England.

For the seven sons of Tancred of Hauteville, a minor Norman nobleman, war was the family business. About 1030 Tancred's two oldest sons, William and Drago, joined other Normans as mercenaries in southern Italy. There they served the Pope and his Lombard allies in attempting to expel the Eastern Roman (Byzantine) Empire--based in Constantinople--from its remaining outposts in Apulia. William d'Hauteville, for reasons perhaps suggested by his nickname "Iron Arm," emerged as leader of the Norman mercenaries. He assumed the title Count and, through the next decade, brought most of Apulia under control of his Norman forces. In later years the d'Hautevilles' personal control over the new principality was strengthened as William and Drago were joined by their brothers, especially the two youngest, Robert "Guiscard" (meaning, "the Resourceful"), who arrived in 1046, and Roger, who joined his older siblings about 1057.

By 1053 Pope Leo IX realized that by encouraging the Normans to oust the Byzantines the Papacy had exchanged a weak and harmless enemy for a powerful and menacing friend. The magnitude of the new problem was exposed in 1053. The Pope determined to nip the nascent power of the Normans in the bud, but the army he sent to achieve that purpose was decisively defeated in a battle at Civitate. Thereafter the Normans, led by the two youngest d'Hautevilles, Robert and Roger, rapidly expanded their power throughout Apulia and added Calabria as well. Finally, in 1059 Pope Nicholas II made the best of a bad situation by creating an alliance of sorts with the d'Hautevilles. In exchange for a nominal commitment of allegiance from the d'Hautevilles, the Pope formally confirmed Robert's claim not only to Apulia and Calabria, but to Sicily as well. Sicily, of course, was actually under Saracen rule; the Pope had in effect granted the Normans a license to conquer the island.

The d'Hautevilles never declined an opportunity for conquest. After a preliminary raid led by Roger with mixed results, the d'Hautevilles launched their invasion of Sicily in 1060--beginning the first Norman Conquest.