This beautiful church is set over the catacombs where St Agnes was buried. It contains Rome’s finest Byzantine mosaic, depicting the saint flanked by popes Honorius and Symmachus. The basilica was under restoration during research, so check it's open before making the trek. Visits to the catacombs must be reserved ahead via email. Nearby is the Mausoleo di Santa Costanza, a circular 4th-century mausoleum with some of Christendom's oldest mosaics.
The original basilica was built in the 4th century for Costanza, daughter of Emperor Constantine. Its remains survive in a field beside the present complex. Abandoned in the 7th century, it was replaced by the current church, later altered over the centuries. It's said that Agnes, aged 13, survived being burned at the stake before being beheaded on Piazza Navona and buried here.