<P> During the 11th century in northern Italy a new political and social structure emerged: the city - state or commune . The civic culture which arose from this urbs was remarkable . In some places where communes arose (e.g. Britain and France), they were absorbed by the monarchical state as it emerged . They survived in northern and central Italy as in a handful of other regions throughout Europe to become independent and powerful city - states . In Italy the breakaway from their feudal overlords occurred in the late 12th century and 13th century, during the Investiture Controversy between the Pope and the Holy Roman Emperor: Milan led the Lombard cities against the Holy Roman Emperors and defeated them, gaining independence (battles of Legnano, 1176, and Parma, 1248; see Lombard League). </P> <P> Similar town revolts led to the foundation of city - states throughout medieval Europe, such as in Russia (Novgorod Republic, 12th century), in Flanders (Battle of Golden Spurs, 14th century) in Switzerland (the towns of the Old Swiss Confederacy, 14th century), in Germany (the Hanseatic League, 14th--15th century), and in Prussia (Thirteen Years' War, 15th century). </P> <P> Some Italian city - states became great military powers very early on . Venice and Genoa acquired vast naval empires in the Mediterranean and Black Seas, some of which threatened those of the growing Ottoman Empire . During the Fourth Crusade (1204), Venice conquered a quarter of the Byzantine Empire . </P> <P> The Maritime Republics were one of the main products of this new civic and social culture based on commerce and exchange of knowledge with other areas of the world outside western Europe . The Republic of Ragusa and the Republic of Venice, for example, had important trade communications with the Muslim and Hindu world and this helped the initial development of the Italian Renaissance . </P>

How did italian city-states like venice and florence became major banking and trade centers