The San Sebastiano catacombs are thought to have developed around a core of three mausoleums (open to visitors), whose origins are believed to date back to the first century of the Empire. They were used firstly by pagans, and later by Christians. The site was covered in the 3C by an esplanade (triclia), then in the 4C by a basilica, which was itself rebuilt in the 17C. The latter now houses a stone bearing what are said to be footprints left by Christ.