The miracle takes place on the anniversary of the martyrdom of San Gennaro (St. Januarius) in September 305 AD.
The first historical reference to the liquefaction of the martyr’s blood is dated 1389. Although now a headline-making saint, little is known about San Gennaro except that he was bishop of Benevento to the south of Naples and was martyred during the persecution of Christians spearheaded by the Roman Emperor Diocletian. According to legend, his body and head, still dripping blood, were gathered up by an old man and taken to a safe place while a local woman filled a phial with his spilt blood.
The dried blood of the saint is preserved in two glass phials and traditionally liquefies three times a year, the Church says, thanks to the devotion and prayers of the faithful. The liquefaction process sometimes takes hours, even days, and on occasions fails to happen at all.