Year 4 (IV) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar (the sources differ, see leap year error for further information) and a leap year starting on Tuesday of the Proleptic Julian calendar. At the time, it was known as the Year of the Consulship of Catus and Saturninus[disambiguation needed] (or, less frequently, year 757 Ab urbe condita). The denomination 4 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.