The interior of the Basilica of St. Mary of the Angels and the Martyrs (Santa Maria degli Angeli e dei Martiri), a titular basilica church, built inside the frigidarium (a large cold pool) of the vast Thermae (Baths) of Diocletian, a Roman Emperor, who ruled from 284 to 305 and had always resisted and persecuted Christianity. The basilica is therefore dedicated to Christian martyrs, both known and unknown.