The catacombs are the ancient underground cemeteries, used by the Christian and the Jewish communities, above all in Rome. The Christian catacombs, which are the most numerous, began in the second century and continued until the first half of the fifth century.In the beginning they were only burial places. Here the Christians gathered to celebrate their funeral rites, the anniversaries of the martyrs and of the dead. During the persecutions, in exceptional cases, the catacombs were used as places of momentary refuge for the celebration of the Eucharist. They were not used as secret hiding places of the early Christians.

This is only a fiction taken from novels or movies. Christian excavators built vast systems of galleries and passages on top of each other. They lie 7-19 metres (23-62 ft) below the surface in area of more than 2.4 square kilometres (590 acres). Narrow steps that descend as many as four stories join the levels. Passages are about 2.5 by 1 metres (8.2 ft x 3.3 ft). Burial niches (loculi) were carved into walls. They are 40-60 centimetres (16-24 in) high and 120-150 centimetres (47-59 in) long. Bodies were placed in chambers in stone sarcophagi in their clothes and bound in linen. Then the chamber was sealed with a slab bearing the name, age and the day of death. After the persecutions, With the edict of Milan, promulgated by the emperors Constantine and Licinius in February 313, the Christians were no longer persecuted. They were free to profess their faith, to have places of worship and to build churches both inside and outside the city, and to buy plots of land, without fear of confiscation. Nevertheless, the catacombs continued to function as regular cemeteries until the beginning of the fifth century, when the Church resumed to bury exclusively above ground or in the basilicas dedicated to important martyrs.

From the time of pope Saint Damasus (366 - 384) they became real shrines of the martyrs, centers of devotion and of pilgrimage for Christians from every part of the empire. The Roman catacombs, of which there are forty in the suburbs, were built along the consular roads out of Rome, such as the Appian way, the via Ostiense, the via Labicana, the via Tiburtina, and the via Nomentana. The Christian catacombs are extremely important for the art history of early Christian art, as they contain the great majority of examples from before about 400 AD, in fresco and sculpture. Amongst the largest and richest in early christian iconography are: catacombs of Domitilla, Sebastian and Callixtus the latter two located on the Appian way.