The Catacombs of Rome are ancient underground burial places under Rome. They were carved in tufa - a soft volcanic rock, outside the walls of the city, since Roman law forbade burial places within city limits.
Though most famous for Christian burials, either in separate catacombs or mixed together, people of all the Roman religions are buried in them, beginning in the 2nd century AD, mainly as a response to overcrowding and shortage of land. The Etruscans, like many other European peoples, used to bury their dead in underground chambers. The original Roman custom was cremation, after which the burnt remains were kept in a pot, ash-chest or urn, often in a columbarium. 

Along with the art at Dura-Europos, the Christian catacombs in Rome are extremely important for the history of Early Christian art, as they contain the majority of examples from before about 400 AD. The Jewish catacombs are similarly important for the study of Jewish culture at this period. From about the 2nd century AD, inhumation (burial of unburnt remains) became more fashionable, in graves or sarcophagi, often elaborately carved, for those who could afford them. Christians also preferred burial to cremation because of their belief in bodily resurrection at the Second Coming.