July 1 – In the Battle of Abritus, the Goths defeat emperor Decius and his son Herennius Etruscus on swampy ground in the Dobruja (Moesia).
In Rome, Hostilian, son of Decius, succeeds his father, while Trebonianus Gallus is proclaimed Emperor by the troops. Gallus accepts him as co-emperor, but an outbreak of plague strikes the city and kills the young Hostilian.
The prosperity of Roman Britain declines during this period as the Germanic tribes of the Franks and Saxons, whose homelands are in Friesland and the Low Countries, make raids around the southeast coast.
Gallus makes peace with the Goths, he permits them to keep their plunder, and offers them a bribe not to return.
A fifteen-year plague begins in the Roman Empire.
The Sassanid king, Shapur I, orders an invasion of the Roman East with the intent of finally capturing the jewel of Syria, Antioch (251–254).
March – Pope Cornelius succeeds Pope Fabian as the 21st pope.
Anthony the Great, Christian saint (d. 356)
July – August
Decius, Roman emperor (killed after the battle of Abritus)
Herennius Etruscus, Roman emperor (killed during the battle of Abritus)
September 7 – Sima Yi, strategist of Wei (b. 179)
Deng Zhi, minister under Liu Bei
Empress Zhen, wife of Cao Fang
Hostilian, Roman emperor (of plague in Rome)
Origen (possible date)
Wang Ling, general of the Kingdom of Wei
Year 251 (CCLI) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Traianus and Etruscus (or, less frequently, year 1004 Ab urbe condita). The denomination 251 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.