Catacombs of San Sebastiano

The site of the Catacomb of St. Sebastian was once a deep depression used as a quarry for pozzolan, known as Ad Catacumbas (meaning "near the cavities"). This term has become synonymous with the underground cemetery. Since the first century, the site has been extensively exploited and built upon. The underground tunnels were repurposed for burial niches, while several columbaria were constructed on the surface. Emperor Constantine (306-337) built a basilica in the shape of a Roman circus.