Besides September and the Saturday before the first Sunday in May, there is a third date when Naples awaits the miracle of the liquefaction of San Gennaro's blood: 16 December, the feast of the Patronage. It commemorates the protection the saint is said to have given the city during the violent eruption of Vesuvius in 1631.
In the Cathedral on Via Duomo the phials are displayed to the faithful in the Royal Chapel of the Treasure of San Gennaro, and during the service led by the Archbishop it is announced whether the blood has liquefied. It is a more intimate occasion than the September feast, but one deeply felt by Neapolitans.
Our tip: arrive in the morning and take the chance to visit the Museum of the Treasure of San Gennaro, next to the Cathedral.