Naples has 450 kms of underground tunnels, aqueducts, and cisterns as well as mausoleums and charnel houses. Close to San Gennaro, the 14th-century cathedral built in homage to the city’s revered patron saint, two tiers of catacombs are built into tufa rock and form the largest ancient Christian burial site outside Rome. These contain ancient tombs, Christian frescoes adorn the vaults, and delicate fifth-century mosaics sparkle in the sepulchral gloom. All Neopolitan bishops were buried here until the 11th century and their tombs were repeatedly looted through the years. Down the street, the church of Santa Maria della Sanità hides the catacombs of Saint Gaudiso, so-named in celebration of a fifth-century saint who founded a monastery here after he was set adrift aboard an old boat in Africa and drifted to Naples. The macabre cemetery at Fontanelle houses the victims of an 18th-century outbreak of cholera, which decimated Naples. There are over 40,000 bones and skulls stacked in a rather rudimentary fashion around the walls in an area roughly covering a soccer field.