|Centuries:||4th century – 5th century – 6th century|
|Decades:||370s 380s 390s – 400s – 410s 420s 430s|
|Years:||403 404 405 – 406 – 407 408 409|
|406 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1159|
|Bahá'í calendar||−1438 – −1437|
|English Regnal year||N/A|
|Chinese calendar||乙巳年 (Wood Snake)
3102 or 3042
— to —
丙午年 (Fire Horse)
3103 or 3043
|- Vikram Samvat||462–463|
|- Shaka Samvat||328–329|
|- Kali Yuga||3507–3508|
|Igbo calendar||−594 – −593|
|Iranian calendar||216 BP – 215 BP|
|Islamic calendar||223 BH – 222 BH|
|Minguo calendar||1506 before ROC
|Thai solar calendar||949|
|Wikimedia Commons has media related to 406.|
Year 406 (CDVI) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Arcadius and Probus (or, less frequently, year 1159 Ab urbe condita). The denomination 406 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.
- Siege of Florence: Stilicho defeats with help from Hunnic forces under Uldin, as well as Alan and Gothic cavalry an army of 20,000 warriors led by Radagaisus. He sends a heavily guarded convoy of provisions into the town and laid siege, by constructing a line of blockhouses, connected by trenches. After two months Stilicho relieves the siege and liberates the city.
- Radagaisus is forced to retreat into the hills of Fiesole. There he tries to escape, but is captured by the Romans.
- August 23 – Radagaisus is executed, 12,000 "barbarians" are incorporated into the Roman army or sold as slaves.
- Autumn – The remaining Roman legions in Britain decided to mutiny. The usurper Marcus is proclaimed emperor.
- The Vandals led by Godigisel are intercepted and defeated by the Franks under Marcomir. Godigisel is killed in battle and succeeded by his son Gunderic.
- December 31 – Vandals, Alans and Suebians cross the Rhine at Mogontiacum (modern Mainz), beginning an invasion of Gaul (traditional date, this may have occurred in 405).
- Fa-Hien, Chinese traveler, arrives in India. He visit the major seats of Buddhist learning (Udyana, Peshawar, and Taxila).
- Hanzei succeeds his brother Richu, and becomes the 18th emperor of Japan.
- Cultivation of rye, oats, hops, and spelt (a wheat used for livestock feed) is introduced into Europe by the invading Vandals, Alans, and Scirii, who also introduce a heavy wheeled plow to be used for farming.
- Attila the Hun, ruler of the Hunnic Empire (approximate date)
- Shao Di, emperor of the Liu Song Dynasty (d. 424)
- Alban of Mainz, priest and martyr (approximate date)
- Godigisel, king of the Vandals
- Gu Kaizhi, Chinese painter (b. c. 344)
- August 23 – Radagaisus, Gothic king
- Zhang Tianxi, ruler of Former Liang (b. 346)