The church was begun in 1226–1265, but was enlarged in the 14th century resulting in the Gothic appearance it has now. However, aspects of the Gothic structure were subsequently destroyed by fires in 1443, 1456 and 1531, and further damage later resulted from military occupation. It is a large edifice built, like many contemporary edifices of the mendicant orders, in bricks, with a lofty bell tower on the left. The interior is on the Egyptian cross plan with a huge nave covered by trusses and with a transept featuring high chapels. The church contains several relics of St. Catherine of Siena, whose family house is nearby.
Interior
Cappella delle Volte
This is an old praying place of Dominican nuns, connected to numerous episode of sanctity of Catherine of Siena's life. It houses the Canonization of St. Catherine by Mattia Preti, flanked by two 1602 paintings by Crescenzio Gambarelli. Other works by the latter are also present. The main wall has a portrait of St. Catherine.
The altars on the right side are decorated by an Appearance of the Virgin by Stefano Volpi, a Nativity of the Virgin by Alessandro Casolani and a reliquary of St. Catherine's relics. They are followed by the St. Catherine Chapel, with, in the centre, an altar housing the saint's head and thumb. Il Sodoma provided a Fainting and Ecstasy of St. Catherine and Death of Niccolò di Tuldo for the chapel, while by Francesco Vanni is a St. Catherine's Exorcism. The 15th-century marble pavement, featuring Orpheus and animals, is attributed to Francesco di Giorgio. The right wall has a fresco by Pietro Lorenzetti and the Adoration of the Shepherds by Francesco di Giorgio, completed by a lunette by Matteo di Giovanni and a predella by Bernardino Fungai.
Transept
On the right transept is altar dedicated to Blessed Ambrogio Sansedoni, also portrayed in a canvas by Francesco Rustici. Notable amongst the chapels are the second, entitled to the martyrs of the German Nation, and the third, which includes a Madonna with Child and the Saint Jerome and John the Baptist by Matteo di Giovanni. The fourth chapel has a Baroque canvas by Raffaello Vanni and a St. Anthony the Abbot from 1426. The Majesty by Guido da Siena is in the centre of the fifth chapel, where are also works by Matteo di Giovanni, Benvenuto di Giovanni and two frescoes by Giuseppe Nicola Nasini. The left transept ends with the altar of St. Dominic.
