Tunnelled out of the Capodimonte hillside in Roman times for use as water cisterns, these labyrinthine catacombs were used as a burial site from the fifth century onwards. In 452, the burial of St Gaudiosus - a North African bishop and hermit - made the site an important shrine. The damp, musty caves have patches of fifth- and sixth-century mosaics, and frescoes from the fifth, 17th and 18th centuries. A fascinating range of burial techniques is in evidence. Note the method used from 1620 to 1650: the corpse was walled upright in a niche with its head cemented into the rear wall. After the bodily fluids had drained away (the malediction puozza sculà, 'may you drain away', is still in use), the headless body was buried and the skull removed, to be repositioned over a frescoed portrait of the illustrious deceased. The remains of St Gaudiosus and the skulls were all transferred to the nearby Cimitero delle Fontanelle during the cholera epidemic of 1974.
In the 17th century, the Dominican friars that tended the chapel of San Gaudioso in the catacombs built the Greek-cross-plan basilica of Santa Maria della Sanità above it. There's a fine Madonna and child with St Hyacinth, St Rosa of Lima and St Agnes by Luca Giordano in the second chapel on the right.
From the transept, steps lead down to the fifth century Cappella di San Gaudioso, which was rebuilt in the tenth and 15th centuries. The church is home to a painting of Mary, found nearby. Rumour has it that after it was discovered, the plague ceased and Mary brought sanità (health) to the area. Another, less comforting, local story has it that Camorra blood giuramenti (blood oaths) took place in the catacombs - a tale that won't be mentioned on the guided tour, although the Sanità is a Camorra stronghold. The hour-long tours leave from the basilica; call ahead to request an English-speaking guide.