Treaty of Melfi

August 23, 1059

Pope Nicholas II invested Robert Guiscard with the duchies of Apulia, Calabria, and the not-yet-conquered Sicily, accepting a Norman vassal in exchange for military support. The formal blessing transformed Norman adventurers into legitimate princes and set up four decades of conquest across the Mezzogiorno and Sicily. The alliance gave the papacy a military counterweight to the German emperor, reshaping the balance of power in Italy.