Catacombe di Domitilla in Rome

You're standing at the entrance to the Catacombs of Domitilla, on the ancient Via Ardeatina in the south of Rome. The Catacombs of St Callixtus are just nearby. What you see up here is only the tip. Beneath your feet runs a maze of tunnels around seventeen kilometres long, on four levels. Roughly fifteen thousand people were buried down there, making this one of the largest catacombs in the city.