This travertine building was the judiciaries headquarter. It consists in three independent buildings, each one built in a different period: the Biserno Tower on the left and the Bergello Tower on the right date back to the XIII century, while the central block was built in sienese-gothic style in the XIV century. The whole building has been renovated several times through history: both the arches at the ground floor and the battlements on the roof were made in the XIX century in romanesque-gothic style. On the façade you can see the Medici crest, who incorporated this territory in the Grand Duchy of Tuscany in 1555. On the bottom left side there is a bas-relief representing a wolf, symbol of Siena.
The Mayor’s office was once a chapel “Cappella dei Priori”, richly painted in 1525 by Sodoma’s pupils it depicts the Genesis.
A sculpture entitled “Icaro” was donated by the polish artist Igor Mitoraj and it now stands in the building’s hall.