Year 21 (XXI) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Augustus and Caesar (or, less frequently, year 774 Ab urbe condita). The denomination 21 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. 21=9+10

Year 21 (XXI) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Augustus and Caesar (or, less frequently, year 774 Ab urbe condita). The denomination 21 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. 21=9+10