A catacomb is an underground cemetery made up of tunnels and rooms carved into rock, where people buried their dead. The most famous catacombs wind beneath Rome and Paris, with passages stretching for miles like an underground maze. Instead of graves in the ground, bodies were placed in slots carved into the walls, stacked from floor to ceiling.

Early Christians in Rome used catacombs starting around 2,000 years ago. At that time, land inside the city was expensive and scarce, but Roman law allowed people to dig burial chambers underground outside the city walls. These passages mainly provided burial places, and some may also have been used as meeting spaces where Christians could worship during periods when their religion faced persecution.

The Roman catacombs contain elaborate artwork: paintings of biblical scenes, symbols like fish and anchors, and inscriptions that tell us about the people buried there. Walking through them today (with a guide, since they're easy to get lost in) feels like stepping into an ancient underground city of the dead.

Paris also has famous catacombs, created in the 1700s when the city's cemeteries became dangerously overcrowded. Workers transferred millions of skeletons into abandoned limestone quarries beneath the streets, arranging the bones in decorative patterns along the walls. Today the word catacomb describes any similar underground burial complex, though the Roman and Parisian examples remain the most striking.