| Millennium: | 1st millennium BC |
|---|---|
| Centuries: | |
| Decades: | |
| Years: |
| 421 BC by topic |
| Politics |
|---|
| Categories |
| Gregorian calendar | 421 BC CDXXI BC |
| Ab urbe condita | 333 |
| Ancient Egypt era | XXVII dynasty, 105 |
| - Pharaoh | Darius II of Persia, 3 |
| Ancient Greek era | 89th Olympiad, year 4 |
| Assyrian calendar | 4330 |
| Balinese saka calendar | N/A |
| Bengali calendar | −1013 |
| Berber calendar | 530 |
| Buddhist calendar | 124 |
| Burmese calendar | −1058 |
| Byzantine calendar | 5088–5089 |
| Chinese calendar | 己未年 (Earth Goat) 2277 or 2070 — to — 庚申年 (Metal Monkey) 2278 or 2071 |
| Coptic calendar | −704 – −703 |
| Discordian calendar | 746 |
| Ethiopian calendar | −428 – −427 |
| Hebrew calendar | 3340–3341 |
| Hindu calendars | |
| - Vikram Samvat | −364 – −363 |
| - Shaka Samvat | N/A |
| - Kali Yuga | 2680–2681 |
| Holocene calendar | 9580 |
| Iranian calendar | 1042 BP – 1041 BP |
| Islamic calendar | 1074 BH – 1073 BH |
| Javanese calendar | N/A |
| Julian calendar | N/A |
| Korean calendar | 1913 |
| Minguo calendar | 2332 before ROC 民前2332年 |
| Nanakshahi calendar | −1888 |
| Thai solar calendar | 122–123 |
| Tibetan calendar | 阴土羊年 (female Earth-Goat) −294 or −675 or −1447 — to — 阳金猴年 (male Iron-Monkey) −293 or −674 or −1446 |
Year 421 BC was a year of the pre-Julian Roman calendar. At the time, it was known in Rome as the Year of the Consulship of Vibulanus and Barbatus (or, less frequently, year 333 Ab urbe condita). The denomination 421 BC 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.