Catacombs of San Callisto, Rome

Along the Appian Way lie the Catacombs of San Callisto, the most important of Rome's early Christian burial grounds—some 20 kilometres of galleries on multiple levels, once holding perhaps half a million tombs. Dug from the late 2nd century into the soft volcanic tufa, they grew as Christianity spread among a still-persecuted community that needed subterranean space to bury its dead according to its beliefs. The 'Crypt of the Popes' held nine 3rd-century pontiffs, and the nearby crypt of St Cecilia preserves early frescoes and symbols—the fish, the anchor, the Good Shepherd—that form the earliest Christian art. Contrary to popular myth, Christians did not usually hide from persecution here, but they did gather to honour their martyrs. Rediscovered in the 19th century, the tunnels reveal the roots of a faith that would remake Rome.