Little is known about the life of Januarius. He is believed to have been martyred in the Emperor Diocletian’s persecution of 305. Legend has it that Januarius and his companions were thrown to the bears in the amphitheater of Pozzuoli, but the animals failed to attack them. They were then beheaded, and Januarius' blood ultimately brought to Naples.
"A dark mass that half fills a hermetically sealed four-inch glass container, and is preserved in a double reliquary in the Naples cathedral as the blood of St. Januarius, liquefies 18 times during the year...Various experiments have been applied, but the phenomenon eludes natural explanation...." [From the Catholic Encyclopedia]
