The 400s was a decade that started on 1 January 400 and ended on 31 December 409.
|Centuries:||4th century – 5th century – 6th century|
|Decades:||370s 380s 390s – 400s – 410s 420s 430s|
|Years:||400 401 402 403 404 405 406 407 408 409|
|Categories:||Births – Deaths – Architecture|
Establishments – Disestablishments
- Constantine III seizes control of the Roman garrison in Britain, declares himself emperor, and crosses into Gaul.
- August 22, 408 – Stilicho, military power behind the imperial throne, is executed. The Roman military is leaderless for several years until Constantius III becomes patrician.
- Construction (and therefore occupation) at Great Zimbabwe begins.
- Validity limit for the information on Eastern Roman Empire in the Notitia Dignitatum.