| Millennium: | 1st millennium |
|---|---|
| Centuries: | 3rd century – 4th century – 5th century |
| Decades: | 370s 380s 390s – 400s – 410s 420s 430s |
| Years: | 397 398 399 – 400 – 401 402 403 |
| 400 by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishment and disestablishment categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 400 CD |
| Ab urbe condita | 1153 |
| Armenian calendar | N/A |
| Assyrian calendar | 5150 |
| Bahá'í calendar | -1444–-1443 |
| Bengali calendar | -193 |
| Berber calendar | 1350 |
| English Regnal year | N/A |
| Buddhist calendar | 944 |
| Burmese calendar | -238 |
| Byzantine calendar | 5908–5909 |
| Chinese calendar | 己亥年十一月十九日 (3036/3096-11-19) — to —
庚子年十一月三十日(3037/3097-11-30) |
| Coptic calendar | 116–117 |
| Ethiopian calendar | 392–393 |
| Hebrew calendar | 4160–4161 |
| Hindu calendars | |
| - Vikram Samvat | 456–457 |
| - Shaka Samvat | 322–323 |
| - Kali Yuga | 3501–3502 |
| Holocene calendar | 10400 |
| Iranian calendar | 222 BP – 221 BP |
| Islamic calendar | 229 BH – 228 BH |
| Japanese calendar | |
| Korean calendar | 2733 |
| Minguo calendar | 1512 before ROC 民前1512年 |
| Thai solar calendar | 943 |
Year 400 (CD) was a leap 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 Stilicho and Aurelianus (or, less frequently, year 1153 Ab urbe condita). The denomination 400 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.