|Centuries:||4th century – 5th century – 6th century|
|Decades:||370s 380s 390s – 400s – 410s 420s 430s|
|Years:||401 402 403 – 404 – 405 406 407|
|404 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1157|
|Chinese calendar||癸卯年 (Water Rabbit)
3100 or 3040
— to —
甲辰年 (Wood Dragon)
3101 or 3041
|- Vikram Samvat||460–461|
|- Shaka Samvat||326–327|
|- Kali Yuga||3505–3506|
|Iranian calendar||218 BP – 217 BP|
|Islamic calendar||225 BH – 224 BH|
|Minguo calendar||1508 before ROC
|Seleucid era||715/716 AG|
|Thai solar calendar||946–947|
Year 404 (CDIV) was a leap year starting on Friday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Honorius and Aristaenetus (or, less frequently, year 1157 Ab urbe condita). The denomination 404 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.
- January 1 – Last known gladiator fight in Rome. This date is usually given as the date of the martyrdom of Saint Telemachus, a Christian monk who was stoned by the crowd for trying to stop a gladiators' fight in a Roman amphitheatre.
- The dome in Ravenna is built by the entire population of the city.
- October 6 – Empress Eudoxia has her seventh and last pregnancy who ends in a miscarriage. She is left bleeding and dies of an infection short after.
- Gwanggaeto the Great of Goguryeo (Korea) attacks Liaodong and takes the entire Liaodong Peninsula.
- The Chinese Buddhist monk Huiyuan, who founded the Pure Land Buddhism sect and the monastery on Mount Lushan, writes the book On Why Monks Do Not Bow Down Before Kings in this year. In his book he argues that although the Buddhist clergy should remain independent and undisturbed by politics, the Buddhist laymen nonetheless make good subjects under monarchs, due to their fear of retribution of karma and desire to be reborn in paradise.
- Eudoxia exiles John Chrysostom, bishop of Constantinople, for criticizing her sumptuous lifestyle. He is banished to the Caucasus in Armenia. Pope Innocent I at Rome orders a synod to reinstate the bishop, but his envoys are imprisoned. Atticus becomes the new bishop of Constantinople.
- October 6 – Aelia Eudoxia, Roman Empress and wife of Arcadius
- Claudian, Roman poet (approximate date)
- Flavian I, Patriarch of Antioch
- He Fani, empress of the Jin dynasty (b. 339)
- Huan Xuan, warlord and emperor of the Jin dynasty (b. 369)
- Paula, Desert Mother and saint (b. 347)
- January 1 – Telemachus, Christian monk and martyr