This brooding fortified church harbours some lovely 13th-century frescoes and a delightful hidden cloister, accessible from the left-hand aisle. The frescoes, in the Oratorio di San Silvestro, depict the story of Constantine and pope Sylvester I and the so-called Donation of Constantine, a notorious forged document with which the emperor supposedly ceded control of Rome and the Western Roman Empire to the papacy.
To access the Oratorio, ring the bell in the entrance courtyard.
The basilica, which dates to the 6th century, took on its present form in the 12th century after the original was destroyed by Normans in 1084. Its name – the Basilica of the Four Crowned Martyrs – is a reference to four Christian sculptors who were supposedly killed by Diocletian for refusing to make a statue of a pagan god.
The basilica's frescoed Aula Gotica (Gothic Hall), on the 1st floor of the Torre Maggiore, is open to bi-monthly guided tours (€10 per person). For details, see www.aulagoticasantiquattrocoronati.it.