Three times a year—the first Saturday in May, September 19, and December 16—all of Naples squeezes into the great cathedral that King Carlo I d’Angio dedicated to San Gennaro in the 13th century. On these dates the dried blood of the city’s patron saint liquefies, or sometimes doesn’t. Not doing so foretells terrible events for Naples, such as the earthquake in 1980 that killed 2,000 residents or an outbreak of the plague in 1528. The rest of the year the blood is kept in a vault inside an altar in the Canella di San Gunnar, where a reliquary houses the head that soldiers of the Emperor Diocletian severed from the rest of the bishop’s body around 305.

Within the cathedral are Naples’ two oldest remaining places of worship. The Capella di Santa Restituta served as the city’s 4th-century basilica and is supported by a forest of columns from a Greek temple, and the Capella di San Giovanni in Fonte was a 5th-century baptistery; if you crane your neck and squint (binoculars or a telescopic lens come in handy) you can make out some endearingly rendered frescoes in the dome, including one showing Christ multiplying the fishes.