| Millennium: | 1st millennium |
|---|---|
| Centuries: | 3rd century – 4th century – 5th century |
| Decades: | 290s 300s 310s – 320s – 330s 340s 350s |
| Years: | 318 319 320 – 321 – 322 323 324 |
| 321 by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishment and disestablishment categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 321 CCCXXI |
| Ab urbe condita | 1074 |
| Armenian calendar | N/A |
| Assyrian calendar | 5071 |
| Bahá'í calendar | -1523–-1522 |
| Bengali calendar | -272 |
| Berber calendar | 1271 |
| English Regnal year | N/A |
| Buddhist calendar | 865 |
| Burmese calendar | -317 |
| Byzantine calendar | 5829–5830 |
| Chinese calendar | 庚辰年十一月十六日 (2957/3017-11-16) — to —
辛巳年十一月廿六日(2958/3018-11-26) |
| Coptic calendar | 37–38 |
| Ethiopian calendar | 313–314 |
| Hebrew calendar | 4081–4082 |
| Hindu calendars | |
| - Vikram Samvat | 377–378 |
| - Shaka Samvat | 243–244 |
| - Kali Yuga | 3422–3423 |
| Holocene calendar | 10321 |
| Iranian calendar | 301 BP – 300 BP |
| Islamic calendar | 310 BH – 309 BH |
| Japanese calendar | |
| Korean calendar | 2654 |
| Minguo calendar | 1591 before ROC 民前1591年 |
| Thai solar calendar | 864 |
Year 321 (CCCXXI) was a common year starting on Sunday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Crispus and Constantinus (or, less frequently, year 1074 Ab urbe condita). The denomination 321 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.