The Blood Miracle
The spire of the Cattedrale di San Gennaro (Naples cathedral)

Saint Januarius is famous for the reputed miracle of the annual liquefaction of his blood, which, according to legend, was saved by a woman called Eusebia just after the saint's death. Thousands of people assemble to witness this event in Naples Cathedral three times a year: on September 19 (Saint Januarius day, to commemorate his martyrdom), on December 16 (to celebrate his patronage of both Naples and of the archdiocese), and on the Saturday before the first Sunday of May (to commemorate the reunification of his relics).[12]
[edit] Description of the ritual

The dried blood is stored in two hermetically sealed small ampoules, held since the 17th century in a silver reliquary between two round glass plates about 12 cm wide. The smaller ampoule, of cylindrical shape, contains only a few reddish spots on its walls (the bulk having allegedly been removed and taken to Spain by Charles III). The larger ampoule, with capacity of about 60 ml and almond-shaped, is about 60% filled with a dark reddish substance.[11][13] Separate reliquaries hold bone fragments believed to be of Saint Januarius.

For most of the time, the ampoules are kept in a bank vault, whose keys are held by a commission of local notables, including the Mayor of Naples; while the bones are kept in a crypt under the main altar of Naples Cathedral. On feast days, all these relics are taken in procession from the cathedral to the Monastery of Santa Chiara, where the archbishop holds the reliquary up and tilts it to show that the contents are solid, and places it on the high altar next to the saint's other relics. After intense prayers by the faithful, including the so-called "relatives of Saint Januarius" (parenti di San Gennaro), the content of the larger vial typically liquefies. The archbishop then holds up the vial and tilts it again to demonstrate that liquefaction has taken place. The announcement of the liquefaction is greeted with a 21-gun salute at the 13th-century Castel Nuovo. The ampoules remain exposed on the altar for eight days, while the priests move or turn them periodically to show that the contents remain liquid.[11]

The liquefaction sometimes takes place almost immediately, but can take hours or even days.

A chronicle of Naples written in 1382 describes the cult of Saint Januarius in detail, but mentions neither the relic nor the miracle.[13][14] The first recorded reference to the 'miracle of the blood' was in 1389.[15][16]