Year 399 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Tribunate of Augurinus, Longus, Priscus, Cicurinus, Rufus and Philo (or, less frequently, year 355 Ab urbe condita). The denomination 399 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.