|Millennium:||1st millennium BC|
|231 BC by topic|
|Gregorian calendar||231 BC|
|Ab urbe condita||523|
|Ancient Egypt era||XXXIII dynasty, 93|
|- Pharaoh||Ptolemy III Euergetes, 16|
|Ancient Greek era||137th Olympiad, year 2|
|Balinese saka calendar||N/A|
|Chinese calendar||己巳年 (Earth Snake)|
2466 or 2406
— to —
庚午年 (Metal Horse)
2467 or 2407
|Coptic calendar||−514 – −513|
|Ethiopian calendar||−238 – −237|
|- Vikram Samvat||−174 – −173|
|- Shaka Samvat||N/A|
|- Kali Yuga||2870–2871|
|Iranian calendar||852 BP – 851 BP|
|Islamic calendar||878 BH – 877 BH|
|Minguo calendar||2142 before ROC|
|Seleucid era||81/82 AG|
|Thai solar calendar||312–313|
−104 or −485 or −1257
— to —
−103 or −484 or −1256
Year 231 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Matho and Maso (or, less frequently, year 523 Ab urbe condita). The denomination 231 BC 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.
- Demetrius II, king of Macedonia, seeks military help from Agron, king of Illyria, a loosely organized state on the Adriatic coast north of Epirus, against the advancing Aetolians. The Illyrian army routs the Aetolians and returns home as the victor.
- The Romans send envoys to Massilia (modern Marseille, France) to negotiate with the Carthaginian general Hamilcar Barca who is based there.
- Hieronymus, tyrant of Syracuse (d. 214 BC)
- Han Xin, prominent Chinese general of the early Han Dynasty is born.