|Centuries:||3rd century – 4th century – 5th century|
|Decades:||290s 300s 310s – 320s – 330s 340s 350s|
|Years:||322 323 324 – 325 – 326 327 328|
|325 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||1078|
|Chinese calendar||甲申年 (Wood Monkey)
3021 or 2961
— to —
乙酉年 (Wood Rooster)
3022 or 2962
|- Vikram Samvat||381–382|
|- Shaka Samvat||247–248|
|- Kali Yuga||3426–3427|
|Iranian calendar||297 BP – 296 BP|
|Islamic calendar||306 BH – 305 BH|
|Minguo calendar||1587 before ROC
|Seleucid era||636/637 AG|
|Thai solar calendar||867–868|
Year 325 (CCCXXV) was a common year starting on Friday of the Julian calendar. At the time, it was known as the Year of the Consulship of Proculus and Paulinus (or, less frequently, year 1078 Ab urbe condita). The denomination 325 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 Constantine I personally assures the security of the Danube frontier by defeating the Goths, the Vandals, and the Sarmatians.
- Licinius is in Thessalonica executed on charge of conspiring, and raising troops against Constantine I.
- Gladiatorial combat is outlawed in the Roman Empire.
- First Council of Nicaea
- April 1 – Crown Prince Jin Chengdi, age 4, succeeds his father Jin Mingdi as emperor of the Eastern Jin dynasty. During his reign he is largely advised by regents, his uncle Yu Liang and high-level officials.
- Constantine the Great, from the Basilica of Maxentius and Constantine, Rome, is started to be made. It is now kept at Palazzo dei Conservatori, Rome.
- May 20 – First Council of Nicaea: Constantine I summons an ecumenical council of bishops in Nicaea (Turkey). The Nicene Creed declares that the members of the Trinity (the Father, the Son, and the Holy Spirit) are equal. The council decides that Easter is celebrated on the first Sunday after the first full moon after the vernal equinox. Arius is exiled to Illyria, his works are confiscated and consigned to the flames.
- The Church of the Nativity is built in Bethlehem.
- Ammianus Marcellinus, Roman historian (approximate date)
- Procopius, usurper of the Roman Empire (approximate date)
- Wang Meng, prime minister of the Former Qin (d. 375)
- October 18 – Jin Mingdi, emperor of the Jin dynasty (b. 299)
- Iamblichus, Syrian philosopher (b. 245)
- Licinius, Roman emperor (executed)
- Sextus Martinianus, Roman Emperor (executed)
- Tuoba Heru, prince of the Tuoba Dai