Forty kilometres of tunnels spiral beneath the Appian Way, holding the remains of half a million souls. The Catacombs of San Callisto alone stretch across four levels, descending twenty metres into volcanic tufa, their galleries carved by Christian communities between the second and fifth centuries. What began as private family burial grounds expanded into labyrinthine necropoleis, their walls lined with loculi — rectangular niches sealed with marble slabs or terracotta tiles — and punctuated by arched cubicula where wealthier families entombed their dead beneath frescoes of the Good Shepherd and Jonah emerging from the whale. Nine popes rest in the Crypt of the Popes within San Callisto, their sarcophagi inscribed in Greek. The Catacombs of Domitilla preserve Rome's oldest known Christian fresco, a second-century depiction of the Last Supper, while the hypogeum of the Flavii family adjoins a fourth-century basilica built directly over the tombs. These subterranean corridors served not only as burial grounds but as sites of clandestine worship during periods of persecution, their narrow passages lit by oil lamps, their walls scratched with anchors, fish, and chi-rho monograms. Evening visits to the catacombs strip away the daylight crowds and amplify the silence. Electric lighting replaced torches in the twentieth century, but the atmosphere remains sepulchral — cool air rises from shafts called luminaria, and the scent of damp tufa lingers. San Sebastiano, the only catacomb that remained accessible throughout the Middle Ages, drew pilgrims who left graffiti invoking Peter and Paul. Priscilla, on the Via Salaria, houses the Cappella Greca, its second-century frescoes depicting a banquet scene that some scholars interpret as an early Eucharist. These underground chambers were never secret. Roman law permitted burial within city walls only in exceptional cases, so Christian and pagan families alike interred their dead along consular roads. The catacombs fell into disuse after the fifth century, when relics were transferred to churches within the city. Rediscovery came in the sixteenth century, when Antonio Bosio mapped the tunnels, and systematic excavation began under Giovanni Battista de Rossi in the nineteenth. Today, a Rome catacombs tour at night offers access to sites that close to general visitors after 17:00, with guides leading small groups through galleries where frescoes glow under directed light and the silence is broken only by footsteps on ancient stone.