Once the Chapter House, its soaring cross-vaults make it Fra Iacopo Talenti da Nipozzano's architectural masterpiece; it was carried out between 1345 and 1355 thanks to the contribution of Florentine merchant Buonamico dé Guidalotti, whose body still lies at rest in front of the altar. The walls and ceiling were frescoed by Andrea di Bonaiuto (1365-67), one of Orcagna's pupils, in a style that shows the influence of the Lorenzettis from Siena.

Inspired by Fra Zanobi dé Guasconi, the cycle contains a refined theological programme which can be reassumed as follows: Christ, the Redeemer of Humanity, generously gives of his grace and doctrine through the Church which, in its turn, contains and stimulates the activity of the Dominican Order. The Basilica of Santa Maria del Fiore is recognizable on the righthand wall with an unusual cupola, quite unlike the one by Brunelleschi, which in fact was not to be carried out until the following century.

This was probably the design for the cupola that Andrea di Bonaiuto presented in 1365 to the Opera del Duomo but which was later rejected. This same fresco, which dipicts the triumphant Church Militant, not only contains portraits of kings, popes and bishops but also many of the glorious men of fame of Florence: Cimabue, Giotto, architects Lapo and Arnolfo di Cambio as well as Boccaccio, Petrarch and Dante Alighieri.