The catacombs were underground burial places for Christians. They were built outside the walls of the city. It was against the law to bury bodies within the city of Rome. Sixty known catacombs can be found along the Appian Way.
The early burial sites were simple marked graves. Later they became large systems of galleries with linking passages.
Bodies were placed in spaces that were between 16 to 24 inches high and 47 to 59 inches long. These spaces were cut in soft tufa rock. Bodies were clothed, wrapped in linen, and sprinkled with ointments. They were then sealed with a slab that was inscribed with the name of the deceased, date of death, and a religious symbol.
When Christianity became the established religion of the Roman Empire in 313 AD, burial places were moved above ground to the cemeteries that we see today.