Emperor Constantine the Great vigorously promotes Christianity, confiscating the property and valuables of a number of pagan temples throughout the Roman Empire.
Constantine I dedicates the Church of the Holy Apostles in Constantinople.
Constantine I promulgates a law against divorce.
Eusebius of Caesarea writes the Onomasticon.
Gregory the Illuminator withdraws to a small sanctuary in the Daranali province (Armenia).
Jovian, Roman Emperor (d. 364)
Julian the Apostate, Roman Emperor (d. 363)
Yao Chang, emperor of the Qiang state Later Qin (d. 394)
Year 331 (CCCXXXI) was a common year starting on Friday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Bassus and Ablabius (or, less frequently, year 1084 Ab urbe condita). The denomination 331 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.