The cathedral built by Bartolommeo Ammanati (1S70), modified by Ippolito Scalza, and completed in 1680 (with the exception of the facade, which is still unfinished) contains a large altar-piece by Taddeo di Bartolo of Siena, and the fragments of an imposing monument erected in1427-1436by the Florentine architect Michelozzo in honour of Bartolommeo Aragazzi, secretary of Pope Martin V., which was taken down in the 18th century.
The atrium has a fresco by Bartolo di Fredi and the two ground-floor halls contain a Coronation of the Virgin by Sano di Pietro and a splendid Resurrection by Sodoma.
In the Sala dei Nove or della Pace above are the noble allegorical frescoes of Ambrogio Lorenzetti representing the effects of just and unjust government; the Sala delle Balestre or del Mappamondo is painted by Simone di Martino (Memmi) and others, the Cappella della Signoria by Taddeo di Bartolo, and the Sala del Consistorio by Beccafumi.
The 14th century gives us Ugolino, Duccio di Buoninsegna, Simone di Martino (or Memmi), Lippo Memmi, Pietro and Ambrogio Lorenzetti, Andrea di Vanni (painter and statesman), Bartolo di Fredi and Taddeo di Bartolo.
In the 15th century we have Domenico di Bartolo, Sano di Pietro, Giovanni di Paolo, Stefano di Giovanni (Il Sassetta) and Matteo and Benvenuto di Giovanni Bartoli, who fell, however, behind their contemporaries elsewhere, and made indeed but little progress.