created to feed the gualchiere (pre-industrial textile machines). After a siege in 1107 by the troops of Matilde of Canossa, the Alberti retreated to their family fortresses in the Bisenzio Valley: Prato could therefore develop as a free commune. Within two centuries it reached 15,000 inhabitants, spurred in by the flourishing textile industry and by the presence of the Holy Belt relic. Two new lines of walls had to be built in the mid-12th century, and in the early 14th century. In 1326, in order to counter the expansionism of the Republic of Florence, Prato submitted voluntarily under the seigniory of Robert of Anjou, King of Naples. However, on 23 February 1351 Joanna I of Naples sold the city to the Republic of Florence in exchange for 17,500 golden florins. Prato's history therefore followed that of Florence in the following centuries. Modern age In 1512, during the War of the Holy League, the city was sacked by Spanish troops assembled by Pope Julius II and the king of Aragón, Ferdinand II, to recover the nearby city of Florence for the Medici family. The severity of the sack of Prato led to the surrender of the Florentine Republic, and to the restoration of the Medici rule. Historians debate the actual number of people killed during the sack, but contemporary chroniclers asserted between 2000 and 6000 people were slaughtered in the streets. In 1653 Prato obtained the status of city and became seat of a Catholic diocese. During the 18th century, with the ascent of Lorraine at the head of the Grand Duchy of Tuscany, the city was embellished and also experienced a significant cultural development, which was promoted by the grand dukes themselves. The intellectual foresight of Prato and its land in this century finds its maximum expression in the words of Filippo Mazzei, a friend of Thomas Jefferson, which today are reported in the second paragraph of the Constitution of the United States of America: All men are created equal. After the unification of Italy in the 19th century, Prato became a primary industrial centre, especially in the textile sector (Italian historian Emanuele Repetti described it as the "Italian Manchester"), and it population grew up to 50,000 in 1901 and to 180,000 in 2001. The town experienced significant internal immigration. Previously part of the province of Florence, in 1992 Prato became the capital of the eponymous province. Climate Prato has