Year 406 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Tribunate of Cossus, Ambustus, Cossus and Potitus (or, less frequently, year 348 Ab urbe condita). The denomination 406 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.