Graciously sitting on banks of the Arno and Serchio Rivers, Pisa has been in existence for at least 35 centuries. Even the ancient Romans called Pisa a very old city. It served as a base for Roman navel expeditions against the Gauls and the Carthaginians and in 180 BC it became a Roman colony. The city became a main sea port as well as a trading center between Sardinia, Corsica and Tuscany. During the 11th century the city became a major commercial center, but it was in constant conflicts and battles with Corsica and Sardinia in order to control the Mediterranean. Through the years Pisa continued to be the center of turmoil and by the 14th century the city was weak; the constant internal struggles had an impact on its future. Florence conquered the city in the 15th century and its role as a major shipping port in the central part of Italy went to Livorno.