The miracle of San Gennaro happens three times a year:
September 19th - Feast day of San Gennaro, which commemorates his martyrdom in 305 AD.
Saturday before the first Sunday in May - Commemoration of the translation of the saint's relics.
December 16th - Celebration of the so-called "secular miracle", which recalls the eruption of Vesuvius in 1631, when the Neapolitans invoked the intercession of San Gennaro to stop the lava flow.
During these dates, the blood contained in two vials stored in the Naples Cathedral liquefies. The miracle is considered a good omen for the city, and its non-occurrence is often viewed with concern.
