On the Arno, 49 m. by rail W. of Florence, is one of the oldest cities in Italy; formerly a port, the river has built up the land at its mouth so that the sea is now 4 m. off, and the ancient trade of Pisa has been transferred to Leghorn. There are a magnificent cathedral, rich in art treasures, a peculiar campanile of white marble which deviates 14 ft. from the perpendicular, known as the leaning tower of Pisa, several old and beautiful churches, a university, school of art, and library. Silks and ribbons are woven, and coral ornaments cut. In the 11th century Pisa was at the zenith of its prosperity as a republic, with a great mercantile fleet, and commercial relations with all the world. Its Ghibelline sympathies involved it in terrible struggles, in which it gradually sank till its fortunes were merged in those of Tuscany about 1550. The council of Pisa, 1409, held to determine the long-standing rival claims of Gregory XII. and Benedict XII. to the Papal chair, ended by adding a third claimant, Alexander V. Pisa was one of the twelve cities of ancient Etruria.