Part of the unfinished nave of what was to have been a new cathedral, the museum contains the Duomo's treasury and some of the original decoration from its facade and interior. The first room on the ground floor displays weather-beaten 13th-century sculptures by Giovanni Pisano (circa 1245–1318) that were brought inside for protection and replaced by copies, as was a tondo of the Madonna and Child (now attributed to Donatello) that once hung on the door to the south transept. The masterpiece is unquestionably Duccio's Maestà, one side with 26 panels depicting episodes from the Passion, the other side with a Madonna and Child Enthroned. Painted between 1308 and 1311 as the altarpiece for the Duomo (where it remained until 1505), its realistic elements, such as the lively depiction of the Christ child and the treatment of interior space, proved an enormous influence on later painters. The second floor is divided between the treasury, with a crucifix by Giovanni
Pisano and several statues and busts of biblical characters and classical philosophers, and La Sala della Madonna degli Occhi Grossi (the Room of the Madonna with the Big Eyes), named after the namesake painting it displays by the Maestro di Tressa, who painted in the early 13th century. The work originally decorated the Duomo's high altar, before being displaced by Duccio's Maestà. There is a fine view from the tower inside the museum.