St Catherine was welcomed into the Dominican fold within this huge and austere 13th-century basilica. Inside, the Cappella di Santa Caterina (halfway down the wall to the right of the altar) contains frescoes by Giovanni Antonio Bazzi (aka Il Sodoma) and Andrea Vanni depicting events in the saint's life. Also here are 15th-century reliquaries containing Catherine's head and one of her fingers, as well as a nasty-looking chain that she is said to have flagellated herself with.
The Cappella delle Volte (Chapel of the Vaults) to the right of the main entrance was where the saint is said to have had many mystical experiences. It now houses a portrait of the saint by her contemporary Andrea Vanni. Other works of note in the basilica include a Nativity by Francesco di Giorgio Martini, a triptych of the Madonna and Child with Saints Jerome and St John the Baptist by Matteo di Giovanni and a Maestà by Guido da Siena.
Modern art in the basilica includes the stained-glass windows by B Cassinari (1982).