Year 373 (CCCLXXIII) 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 Augustus and Valens (or, less frequently, year 1126 Ab urbe condita). The denomination 373 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.
|Ab urbe condita||1126|
|Balinese saka calendar||294–295|
|Chinese calendar||壬申年 (Water Monkey)|
3069 or 3009
— to —
癸酉年 (Water Rooster)
3070 or 3010
|- Vikram Samvat||429–430|
|- Shaka Samvat||294–295|
|- Kali Yuga||3473–3474|
|Iranian calendar||249 BP – 248 BP|
|Islamic calendar||257 BH – 256 BH|
|Minguo calendar||1539 before ROC|
|Seleucid era||684/685 AG|
|Thai solar calendar||915–916|
499 or 118 or −654
— to —
500 or 119 or −653
- Emperor Valens is converted to Arianism and orders the persecution of Trinitarian Christians in the Roman East.
- Quintus Aurelius Symmachus becomes proconsul of Africa, and is made a member of the pontifical college.
- Count Theodosius is appointed commander of an expedition to suppress the rebellion of Firmus in Mauretania.
- Valens Aqueduct is inaugurated near Constantinople (modern Istanbul); the aqueduct has a length of 971 meters.
- Battle of the Tanais River: The Huns defeat the Alans near the Don, sending the remnants fleeing westward.
- King Shapur II declares war as a result of Valens' support of Armenia. Emperor Valens makes Antioch his military base for the campaign against Persia.
- May 2 – Athanasius of Alexandria, Egyptian Coptic Orthodox bishop, opponent of Arianism and saint (b. 296)
- June 9 – Ephrem the Syrian, Syrian Orthodox priest and saint (b. 306)
- November 19 – St. Nerses I