400s (400–409 CE)

Decade in Late Antiquity marked by rivalry within the Roman Empire, Gothic campaigns under Alaric, military crises in Italy and Gaul, and events that accelerated the transformation of Western Europe.

Overview

The 400s (400–409 CE) is a decade in the late Roman Empire during the broader period historians call Late Antiquity. The empire was governed as two courts under the sons of Theodosius I: Honorius in the West and Arcadius in the East. Central political authority was fragile and military strongmen, frontier pressures, and migrating peoples shaped events across the Mediterranean and western Europe.

Political and military developments

This decade was dominated by military crisis and maneuvering. In the Western empire the magister militum Stilicho exercised great influence as the chief military commander and de facto guardian of Honorius. The Visigothic leader Alaric campaigned in the Balkans and Italy, prompting Roman responses that included the battles of Pollentia and Verona (402), where Roman forces checked his advances without permanently removing the Gothic threat.

Other major movements included the invasion led by the Gothic king Radagaisus into Italy (405–406), which was defeated by Stilicho, and a mass crossing of Germanic and other tribal groups across the frozen Rhine into Gaul in the winter of 406/407 (often dated to 31 December 406). In Britain and Gaul the usurper Constantine III declared himself emperor in 407 and established a short-lived power base that further weakened central control.

Eastern empire and succession

On the eastern side Arcadius remained emperor until his death in 408, after which his son Theodosius II—born during this decade—succeeded as a child emperor. Power in Constantinople was exercised through court officials and regents, illustrating how imperial legitimacy and practical rule increasingly depended on influential ministers and military leaders rather than sole dynastic authority.

Society, religion and culture

The period continued the Christianization of imperial institutions and society: bishops gained greater civic roles, Christian doctrine shaped law, and monasticism spread across the empire. At the same time classical civic life and municipal finances were under strain from taxation, military requisitions, and population movements, contributing to long-term regional transformations.

Legacy and notable facts

The decade set the stage for further disintegration of Western Roman authority in Gaul, Spain and Britain and foreshadowed the Sack of Rome in 410.
Key figures include the generals Stilicho and Constantine III, the Gothic leader Alaric, and the child-emperor Theodosius II.
The Rhine crossing of 406 and the repeated invasions of Italy marked turning points in the Migration Period that reshaped western Europe.