San Gennaro was Bishop of Benevento, Italy, and died a martyr in 305 AD during a religious persecution spearheaded by Emperor Diocletian. He signed his death warrant when he visited the deacons, Sosso and Proculo, and the laymen, Eutichete and Acuzio, in jail. The Proconsul, Timothy, had Gennaro arrested. He was tortured without wavering in his resolution to remain loyal to Christ.

He was thrown headlong into a furnace, but according to legend, he came through unscathed. Furious, the agents beheaded him. His body and the severed head, still dripping blood, were gathered up by an elder who wrapped them reverently in a cloth. A Neapolitan woman collected the blood with a sponge and filled a phial with the precious liquid.