An underground burial gallery, especially in early Christian Rome. Catacombs were named after the best known example, St Sebastian in the Hollow (ad Catacumbas). Forty such subterranean chambers are known in Rome, tunnelled through soft rock outside the ancient city boundaries. The anniversaries of martyrs were celebrated at the graves. Looted by barbarians and subject to collapse, they were virtually forgotten until their accidental rediscovery in the 16th century. Similar ones are also found as far apart as Salzburg and Malta.