An underground cemetery of connecting passageways with recesses for tombs.
Example:
The early Christian catacombs of Rome provide a striking glimpse into the ancient past for modern-day visitors.
About forty Christian catacombs have been found near the roads that once led into Rome. After the decline of the Roman empire these cemeteries were forgotten, not to be rediscovered until 1578. Catacomb has come to refer to different kinds of underground chambers and passageways. The catacombs of Paris are abandoned stone quarries that were not used for burials until 1787.