On the first floor of the Palace is seated the Museum, where we find exhibited masterpieces of the Sienese school (XIV-XVI century), sculptures, goldsmith's art, coins, arms, earthenware and ceramics.
The Sala del Mappamondo (the World Map Room), used to be the headquarters of the Council of the Republic. The room was so-called after the enormous wooden disc by Ambrogio Lorenzetti, depicting the territory of the Republic. The grandiose Maestà by Simone Martini (1315 and 1321) stands out as one of the greatest masterpieces of European gothic art, a work that represents the great and evolved civility of the Sienese 1300s and is more advanced in the pictorial and spatial conception than the much more famous Maestà by Duccio di Buoninsegna, which is kept in the Opera del Duomo.
Here the virgin is no longer depicted in the cold and hieratic forms of Byzantine painting, but, thanks to a hazy drawing and to the use of warmer, softer colours, the virgin is enriched with an intense and deep humanity. The celestial court that surrounds her is also portrayed in a new way; single characters each assume their own pose and no longer belong to an indistinct togetherness of motionless figures. On the opposite walls is another masterpiece by Simone Martini, the very famous Guidoriccio da Fogliano, emblem of the virtue and civil power of the old Republic of Siena.
Adjacent ot the Sala del Mappamondo is the Room of the Government of the Nine, called the Sala della Pace. The nine judges that governed Siena from 1292 to 1355 met here – in fact, they could never leave the Palace, except on public holidays. On three sides of the room is the fresco, the very famous cycle of Allegoria del Buono e del Cattivo Governo, work of Ambrogio Lorenzetti.
Commissioned by the Government of the Nine between 1338 and 1340, the work, in its representation of binomial peace and war, celebrates a tight political will to maintain peace and stability. On the central walls the just governor, depicted in the shoes of an old sage with the wolf and twins, symbol of Siena, at his feet, sits between the virtues that keep watch over the good government, represented in the form of young women: the virtues of peace, that gives its name to the room, strength, prudence, magnanimity, truth, temperance and justice. On the side walls you can observe the effects of the good government, in the images of an industrious and smiling medieval city, as wells as those, tragic and terrible effects of the bad government, personified as a dark and fearful demon.