阳金龙年 (male Iron-Dragon) 147 or −234 or −1006 — to — 阴金蛇年 (female Iron-Snake) 148 or −233 or −1005
AD 21 (XXI) was a common year starting on Wednesday of the Julian calendar. At the time, it was known as the Year of the Consulship of Tiberius and Drusus (or, less frequently, year 774 Ab urbe condita). The denomination AD 21 for this year has been used since the early medieval period, when the Anno Dominicalendar era became the prevalent method in Europe for naming years.