boosted scientific and artistic advancement. Thanks to their favorable position between East and West, Italian cities such as Venice became international trading and banking hubs and intellectual crossroads. Milan, Florence and Venice, as well as several other Italian city-states, played a crucial innovative role in financial development, devising the main instruments and practices of banking and the emergence of new forms of social and economic organization. During the same period, Italy saw the rise of the Maritime Republics: Venice, Genoa, Pisa, Amalfi, Ragusa, Ancona, Gaeta and the little Noli. From the 11th to the 13th centuries these cities built fleets of ships both for their own protection and to support extensive trade networks across the Mediterranean, leading to an essential role in the Crusades. The maritime republics, especially Venice and Genoa, soon became Europe's main gateways to trade with the East, establishing colonies as far as the Black Sea and often controlling most of the trade with the Byzantine Empire and the Islamic Mediterranean world. The papacy regained its authority, and started a long struggle with the empire, about both ecclesiastical and secular matters. The first episode was the Investiture Controversy. In the 12th century those Italian cities which lay in the Holy Roman Empire launched a successful effort to win autonomy from the Holy Roman Empire. In the north, a Lombard League of communes launched a successful effort to win autonomy from the Holy Roman Empire, defeating Emperor Frederick Barbarossa at the Battle of Legnano in 1176. This made north Italy a land of quasi-independent or independent city-states until the 19th century (see Italian city-states and history of every city). The revolts were funded by the Byzantine Empire, which hoped to expel the Germanic peoples from Italy; this sponsorship was, like the invasion of the south, part of a 12th-century Byzantine effort to regain the influence it had once held on the peninsula during the reign of Justinian I. In the 11th century, the Normans occupied the Lombard and Byzantine possessions in Southern Italy, ending the six century old presence of both powers in the peninsula. The independent city-states were also subdued. During the same century, the Normans also ended Muslim rule in Sicily. Norman rule in what had once been Byzantine territory naturally angered Constantinople, which in 1155 made a last attempt under Emperor Manuel I Komnenos to reassert its authority in Southern Italy. However, the attempt failed,