Year 171 (CLXXI) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Severus and Herennianus (or, less frequently, year 924 Ab urbe condita). The denomination 171 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.