Januarius is the name of a month in the ancient Roman calendar, called January in English.

Januarius, or Gennaro, bishop of Benevento, is a saint and martyr in both the Roman Catholic and Eastern Orthodox traditions. According to legendary sources, he died during the persecution of Diocletian near Puteoli at the sulphur mines, where he was visiting imprisoned deacons. His body was later transferred to Naples, of which he is now the patron saint.

He retains his feast day, September 19, in the calendar of the Catholic Church and in the New Calendar of the Orthodox Church, despite very limited information about his life and works, primarily due to the reputed miracle of the liquefication of his blood. The dried blood is stored in small capsules in a reliquary. When these capsules are brought into the vicinity of his body on his feast day or on the Saturday before the 1st Sunday in May, the dried blood becomes inexplicably liquid. Thousands of persons witness this event each year.

See also Feast of San Gennaro