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|401 by topic|
|Ab urbe condita||1154|
|Balinese saka calendar||322–323|
|Chinese calendar||庚子年 (Metal Rat)|
3097 or 3037
— to —
辛丑年 (Metal Ox)
3098 or 3038
|- Vikram Samvat||457–458|
|- Shaka Samvat||322–323|
|- Kali Yuga||3501–3502|
|Iranian calendar||221 BP – 220 BP|
|Islamic calendar||228 BH – 227 BH|
|Minguo calendar||1511 before ROC|
|Seleucid era||712/713 AG|
|Thai solar calendar||943–944|
527 or 146 or −626
— to —
528 or 147 or −625
Year 401 (CDI) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Vincentius and Fravitus (or, less frequently, year 1154 Ab urbe condita). The denomination 401 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.
- Emperor Arcadius sends many gifts to the Hunnish chieftain Uldin, in appreciation of his victory over the Goths and Gainas. Arcadius then allies himself with the Huns.
- Piracy is committed by slave-traders from Galatia (Turkey), along the coasts of Africa. The old Legio II Adiutrix, part of which had always been stationed at Aquincum (modern Budapest), is divided into two comitatenses and shipped to Britannia.
- Stilicho, Roman general (magister militum), leads his army in an extensive campaign against the Vandals in Rhaetia (Switzerland).
- The Temple of Artemis near Selçuk in Ephesus is dismantled.
- November 18 – The Visigoths, led by king Alaric I, cross the Alps and invade northern Italy. Emperor Honorius moves his capital to the coastal city of Ravenna, which is protected by marshes and strong fortifications. Stilicho begins the process of reclaiming the city.
- Kumarajiva, Kuchean Buddhist monk, arrives in Chang'an and begins translating Buddhist texts into Chinese.
- December 19 – Pope Anastasius I dies at Rome after a 2-year reign, and is succeeded by Innocent I as the 40th pope proclaiming his universal power over the whole of Christendom.
- The Mahabharata, an Indian Sanskrit epic, is finalised.
- Aelia Eudocia, Roman Empress and wife of Theodosius II (approximate date)
- Leo I, Byzantine Emperor (d. 474)
- April 10 – Theodosius II, Roman Emperor (d. 450)
- December 19 – Pope Anastasius I
- Duan Ye, prince of the Chinese state Northern Liang
- Lü Zuan, emperor of the Di state Later Liang
- Murong Sheng, emperor of the Xianbei state Later Yan (b. 373)
- Empress Yang, wife of Lü Zuan