The limits on the Roman town, were the earliest known walls to the city. During the 10th and 11th centuries, the town grew to the east and later to the north, in what is now the Camollia district. Walls were built to totally surround the city, and a second set was finished by the end of the 13th century. Much of these walls still exist today.
Siena's university, founded in 1240 and famed for its faculties of law and medicine, is still among the most important Italian universities. Siena rivalled Florence in the arts throughout the 13th and 14th centuries: the important late medieval painter Duccio di Buoninsegna (1253–1319) was a Sienese, but worked across the peninsula, and the mural of "Good Government" by Ambrogio Lorenzetti in the Palazzo Pubblico, or town hall, is a magnificent example of late-Medieval/early Renaissance art as well as a representation of the utopia of urban society as conceived during that period. Siena was devastated by the Black Death of 1348, and also suffered from ill-fated financial enterprises. In 1355, with the arrival of Charles IV of Luxembourg in the city, the population rose and suppressed the government of the Nove (Nine), establishing that Dodici (Twelve) nobles assisted by a council with a popular majority. This was also short-lived, being replaced by the Quindici (Fifteen) reformers in 1385, the Dieci (Ten, 1386–1387), Undici (Eleven, 1388–1398) and Twelve Priors (1398–1399) who, in the end, gave the city's seigniory to Gian Galeazzo Visconti of Milan in order to defend it from the Florentine expansionism.