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Year 431 (CDXXXI) was a common year starting on Thursday of the Julian calendar. At the time, it was known as the Year of the Consulship of Bassus and Antiochus (or, less frequently, year 1184 Ab urbe condita). The denomination 431 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.

• Aetius campaign in the Alps: Flavius Aetius, Roman general (magister militum), fights the rebellion in Rhaetia (Switzerland) and Noricum (Austria). He is attested in the city of Vindelicia (modern Augsburg), reestablishing Roman rule on the Danube frontier.
• Aetius pushes the Salian Franks back across the River Somme. King Chlodio signs a peace treaty and becomes a foederatus of the Western Roman Empire.^{[citation needed]}

• Hippo Regius becomes the capital of the Vandal Kingdom. After 14 months of hunger and disease, the Vandals ravage the city. Emperor Theodosius II sends an imperial fleet with an army under command of Aspar, and lands at Carthage.
• Aspar is routed by the Vandals and Flavius Marcian, future Byzantine emperor, is captured during the fighting. He negotiates a peace with King Genseric and maintains imperial authority in Carthage.^{[citation needed]}

• March 10 – Kʼukʼ Bahlam I, the first known ruler of the Mayan city-state of Palenque (the modern-day state of Chiapas in southern Mexico) comes to power and reigns until his death four years later.^[1]
• Possible date of the Tierra Blanca Joven (TBJ) eruption of the Ilopango caldera in central El Salvador.

• Greek Neoplatonist philosopher Proclus begins studying at the Academy in Athens.

• June – First Council of Ephesus: Nestorianism is rejected; the Nicene Creed is declared to be complete. Nestorius is deposed from his see.
• October 1 – Maximianus is enthroned as Patriarch of Constantinople.
• Pope Celestine I dispatches Palladius to serve as bishop to the Irish.

• Anastasius I, emperor of the Byzantine Empire (approximate date)
• Odoacer, first "barbarian" king of Italy (d. 493)

• June 22 – Paulinus of Nola, Christian bishop and poet (b. 354)
• Qifu Mumo, prince of the Chinese Xianbei state Western Qin