Year 403 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Tribunate of Mamercinus, Varus, Potitus, Iullus, Crassus and Fusus (or, less frequently, year 351 Ab urbe condita). The denomination 403 BC 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.