Completed in 1324 on the orders of Charles I of Anjou, this was the royal church of the Angevins. Pietro Cavallini's frescoes in the Cappella Brancaccio are among the few surviving 14th-century remnants. Take the guided tour (in Italian, with an English information sheet) to view the sacristy, crowned by a ceiling fresco by Francesco Solimena and home to the sarcophagi of 45 Aragon princes and other nobles. The tour includes a peek at rare historical garments retrieved from the coffins.
The longer tour (adult/reduced €7/5) also takes in the former monastic cell of St Thomas Aquinas, where you can still see the bell he would ring to call his students. English-language guides are available but need to be requested in advance (by email via the website).
Back in the church, the Cappellone del Crocifisso is home to the miraculous 13th-century Crocifisso tra La Vergine e San Giovanni, said to have spoken to St Thomas Aquinas. It asked him: 'Bene scripsisti di me, Thoma; quam recipies a me pro tu labore mercedem?' (You've written good things about me, Thomas; what will you get in return?) – 'Domine, non aliam nisi te' (Nothing if not you, O Lord), Thomas replied diplomatically. The first bishop of New York, Richard Luke Concanen (1747–1810) is also buried in the church.