These catacombs are often packed with tour-bus groups, and they run perhaps the most standard tour, but the funerary tunnels are phenomenal. They’re the first cemetery of the Christian community of Rome, and burial place of 16 popes in the 3rd century. They bear the name of St. Callixtus, the deacon whom Pope St. Zephyrinus put in charge of them and who was later elected pope (a.d. 217–22) himself. The complex is a network of galleries structured in four levels and reaching a depth of about 20m (65 ft.), the deepest in the area. There are many sepulchral chambers and almost half a million tombs of early Christians.
Entering the catacombs, you see the most important crypt, concealing the remains of nine popes. Some of the original marble tablets of their tombs are preserved. Also commemorated is St. Cecilia, patron of sacred music (her relics were moved to her church in Trastevere during the 9th c.). Farther on are the Cubicles of the Sacraments, with 3rd-century frescoes.