| 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 |
| Bahá'í calendar | -1523 – -1522 |
| Bengali calendar | -272 |
| Berber calendar | 1271 |
| 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 | |
| - Bikram Samwat | 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 |
| Thai solar calendar | 864 |