|Millennium:||1st millennium BC|
|257 BC by topic|
|Gregorian calendar||257 BC|
|Ab urbe condita||497|
|Ancient Egypt era||XXXIII dynasty, 67|
|- Pharaoh||Ptolemy II Philadelphus, 27|
|Ancient Greek era||130th Olympiad, year 4|
|Balinese saka calendar||N/A|
|Chinese calendar||癸卯年 (Water Rabbit)|
2440 or 2380
— to —
甲辰年 (Wood Dragon)
2441 or 2381
|Coptic calendar||−540 – −539|
|Ethiopian calendar||−264 – −263|
|- Vikram Samvat||−200 – −199|
|- Shaka Samvat||N/A|
|- Kali Yuga||2844–2845|
|Iranian calendar||878 BP – 877 BP|
|Islamic calendar||905 BH – 904 BH|
|Minguo calendar||2168 before ROC|
|Seleucid era||55/56 AG|
|Thai solar calendar||286–287|
−130 or −511 or −1283
— to —
−129 or −510 or −1282
Year 257 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Regulus and Blasio (or, less frequently, year 497 Ab urbe condita). The denomination 257 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.
- The Romans attack Sardinia and try to capture it from the Carthaginians.
- The Battle of Tyndaris is fought between the Roman fleet (with Marcus Atilius Regulus in command) and Carthaginian fleet off Tyndaris (modern Tindari) in Sicily. Hiero II, tyrant of Syracuse, has allowed Tyndaris to be a base for the Carthaginians. However, after this battle, the town falls to Roman forces.
- Thục Phán (An Dương Vương), Chief of the Thục Tribe of the Âu Việts, defeats the Văn Lang Confederacy and unifies all Âu Việt and Lạc Việt tribes, thus founding the Kingdom of Âu Lạc and the Thục Dynasty.