Between XI and X centuries some Italian coastal cities (Amalfi, Pisa, Genoa and Venice) became indipendent and expanded their commercial activities in the Mediterranean Sea. The power of Pisa and Genoa started to rise during XI century when they won some important victories against the Saracen pirates. These were forced to give up their bases in Sardinia and Corsica to the two maritime cities (Pisa, Genoa). The alliance between Pisa and Genoa  turned into open war in 1284 when ,at Meloria, a small island in front of Leghorn ( Livorno ) the Genoese fleet defeated the Pisan one. So Genoa became the ruler of the Tyrrhenian Sea whereas in the Adriatic Sea, there was a much more fearful rival, the Venetian Republic. The war started in 1298 with a naval battle near the island of Curzola was won by the Genoese. This war went on until 1378 when, after the war with Chioggia which was won by the Venetians, a peace treaty was signed in favour of Venice

In 991 Venice signed a commercial treaty with the Saracens, initiating the Venetian policy of trading with the Muslim rather than fighting them. The Crusades and the resulting development of trade with Asia led to the establishment of Venice as the greatest commercial centre for trade with the East. The republic profited greatly from the partition of the Byzantine Empire in 1204 and became politically the strongest European power in the Mediterranean. In the 13^th and 14^th centuries Venice was involved in a series of wars with Genoa, its chief commercial rival. In the war of 1378-1381, Genoa was compelled to acknowledge Venetian supremacy. Wars of conquest enabled Venice to acquire neighbouring territories, and by the late 15^th century the city-state was the leading maritime power in the Christian world. The beginning of Turkish invasions in the middle of the 15^th century marked the decline of Venetian supremacy. Thereafter, faced with attacks by foreign invaders and other Italian states, its power waned, and the discovery of a sea route to the Indies around the Cape of Good Hope by the Portuguese navigator Vasco da Gama in 1497-1498 accelerated the decline. The wealth of Venice depended on the commercial activities it developed. In the 14^th and 15^th centuries no other European city could compare with Venice commercial traffics: it hold the supremacy of the commerce of the most precious oriental products. Its merchant ships carried silk from China, carpets from Persia, spices from the Indies, perfumes from Arabia. Its naval dockyard built a galley a day: a primacy never beaten by any other maritime city in Europe at those times. The riches produced by its commercial traffics allowed the Venetian government to build splendid monuments and buildings. After the fourth Crusade (13^th century), Venice had the monopoly of the trade of oriental products. In order to protect their maritime trades, Venetians organized a service of coastguard vessels composed of ten ships on patrol, searching the seas sailed by the Venetian merchant ships. Venice commercial power declined after the discovery of America, which turned the traffics from the Mediterranean to the Atlantic Ocean.