Siena was founded in I B.C. as a Roman colony. It was then occupied by the Lombards and later conquered by the Franks. After a series of wars with Florence, the city grew considerably in wealth and power until it was defeated at Colle Val d’Elsa by Charles of Anjou. Its demographic and artistic development however continued during the period of the Guelph government, when the main buildings in the city were constructed (Palazzo Pubblico, the Mangia Tower, the Cathedral, the churches of San Domenico and San Francesco). A serious plague epidemic broke out in 1348. It became an independent Republic under the government of the Petrucci family in 1487, only to be besieged by Spanish troops in 1550. Siena fell into the hands of Cosimo I dei Medici in 1557 and, after the Grand Duchy of Tuscany was inherited by the Hapsburg-Lorraines, saw a rebirth of its economic activities and the reform of its administrative institutions. The railway line was built in 1850 and helped to speed up the modernisation process as well as contributing towards the expansion of the city outside the ancient walls.