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|Centuries:||1st century – 2nd century – 3rd century|
|Decades:||90s 100s 110s – 120s – 130s 140s 150s|
|Years:||118 119 120 – 121 – 122 123 124|
|121 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||874|
|Chinese calendar||庚申年 (Metal Monkey)
2817 or 2757
— to —
辛酉年 (Metal Rooster)
2818 or 2758
|Coptic calendar||−163 – −162|
|- Vikram Samvat||177–178|
|- Shaka Samvat||42–43|
|- Kali Yuga||3221–3222|
|Iranian calendar||501 BP – 500 BP|
|Islamic calendar||516 BH – 515 BH|
|Minguo calendar||1791 before ROC
|Seleucid era||432/433 AG|
|Thai solar calendar||663–664|
Year 121 (CXXI) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Verus and Augur (or, less frequently, year 874 Ab urbe condita). The denomination 121 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.
- Roman settlement in present-day Wiesbaden, Germany is first mentioned.
- Emperor Hadrian fixes the border between Roman Britain and Caledonia on a line running from the River Tyne to the Solway Firth.
- Construction of the Temple of Venus and Roma begins in Rome.
- Era name changes from Yongning (2nd year) to Jianguang in the Chinese Eastern Han Dynasty.