The Catacombs of San Gennaro are an ancient underground cemetery in Naples, Italy, located on the slopes of Capodimonte Hill. The catacombs are named after Saint Januarius (San Gennaro), the patron saint of Naples, whose remains were once interred there.

The catacombs were used as a burial site from the 2nd century AD to the 5th century AD, and it is estimated that more than 3,000 tombs were created there during that time. The catacombs consist of two levels, with the upper level being the oldest and containing the oldest Christian tombs. The lower level was created later and contains more elaborate tombs and decorations.

The catacombs are decorated with frescoes, mosaics, and sculptures that depict scenes from the Bible, as well as images of the saints and the martyrs. The catacombs also contain a number of early Christian symbols, such as the fish, the dove, and the anchor.

The catacombs were rediscovered in the 17th century and have since become a popular tourist attraction. They are open to the public and can be visited with a guided tour. The site also includes a small museum that displays some of the artifacts and objects found in the catacombs.