Normans first arrived in Italy as pilgrims, probably on their way to or returning from either Rome or Jerusalem, or from visiting the shrine at Monte Gargano, during the late tenth and early eleventh centuries.
In 1017, the Lombard lords in Apulia recruited their assistance against the dwindling power of the Byzantine Catapanate of Italy.
Italo-Normans were the primary Norman mercenaries in the employ of the Byzantine emperors, and many found service in Rome under the pope.
When founded in 1130, this Italo-Norman kingdom united the whole of Southern Italy under the same rule for the first time since Justinian's brief reconquest of the peninsula as a whole.
After the latter's death without heirs in 1189, and following the brief reign of his illegitimate cousin Tancred of Lecce, the German Emperor Henry VI of Swabia (who had married Constance, aunt and legitimate successor of William II) conquered the kingdom in 1194, defeating William III of Sicily (son of Tancred) and ending the Italo-Norman dynasty.