400s

The 400s was a decade that started on 1 January 400 and ended on 31 December 409.

Events
 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.