These days it retains its government functions and also houses the city museum, Museo Civico, which is well worth a visit for its frescoes, paintings and sculptures. The Sienese school was artistically significant and the late medieval frescoes were some of the first to depict non-religious themes. Instead they made statements about government, justice and patriotic devotion. The most significant is the huge fresco cycle of 1337 by Ambrogio Lorenzetti, entitled Allegory of Good and Bad Government; it’s not difficult to get the painting’s message.
The city was not turning its back on religion completely and there are also striking paintings of the Virgin including Simone Martini’s Maesta (Virgin Mary in Majesty), his first known canvas dating from 1315, and also Taddeo di Bartolo’s Storie della Madonna of 1407, depicting stories from the life of the Virgin Mary. Dating from much later, you’ll even find frescoes depicting the Unification of Italy in the late 19th century. Museo Civico is history in art.