St Januarius

St. Januarius (San Gennaro) is a patron saint of and former bishop of Naples in the 4th century. Januarius and his friends were initially sentenced to be eaten by the lions, tigers, and bears at the Naples amphitheater. Although the beasts had been starved for several days before the day of the planned transformation of the Christians into animal crackers, the beasts refused to attack Januarius and his colleagues. The spectators at the amphitheater were frightened by the indifference of the starving animals to the Christians and rumors began to circulate that the Christians had magical powers and were possibly protected by their god. The governor of Campania ordered their immediate beheading and Januarius' body was later returned to the Cathedral in Naples.
Over a century later, it was purported that a vial of St. Januarius' blood surfaced and was preserved and permanently fixed in the metal reliquary in the Cathedral of Naples. Thousands of people assembled to witness this event in the 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). 

The Cardinal of Naples shows the liquified vial of San Gennaro's blood.

Sometimes the "blood" liquefies immediately, other times it takes hours. When the Cardinal brings the vial to the altar that holds the saint's blood, the people, who gather by the thousands, pray that the blood becomes liquid once again. If the miracle takes place, the officiant proclaims, "Il miracolo é fatto!" and waves a white handkerchief. Then a Te Deum is sung and the reliquary is taken to the altar rail so the faithful can kiss the vial. The priest conducting the service chants "The miracle has happened." The choir and the congregation respond with a Te Deum, and prayers are offered to St. Januarius. There have been a few instances when the substance in the vial had not liquefied and the faithful believes that it is a sign of impending peril. Five times when liquefaction has failed there have been major disasters, the latest being an earthquake in southern Italy that killed 3,000 people in 1980.