Catacombs, human-made subterranean passageways for religious practice. Any chamber used as a burial place can be described as a catacomb, although the word is most commonly associated with the Roman empire

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

. Many are under cities and have been popularized by stories of their use as war refuges, smugglers' hideouts, or meeting places for cults.
The first place to be referred to as catacombs was the system of underground tombs between the 2nd and 3rd milestones of the Appian Way

Appian Way

The Appian Way was one of the earliest and strategically most important Roman roads of the ancient republic. It connected Rome to Brindisi, Apulia, in southeast Italy...

 in Rome

Rome

Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...

, where the bodies of the apostles Peter and Paul, among others, were said to have been buried.