|Millennium:||1st millennium BC|
|300 BC by topic|
|Gregorian calendar||300 BC|
|Ab urbe condita||454|
|Ancient Egypt era||XXXIII dynasty, 24|
|- Pharaoh||Ptolemy I Soter, 24|
|Ancient Greek era||120th Olympiad (victor)¹|
|Balinese saka calendar||N/A|
|Chinese calendar||庚申年 (Metal Monkey)|
2397 or 2337
— to —
辛酉年 (Metal Rooster)
2398 or 2338
|Coptic calendar||−583 – −582|
|Ethiopian calendar||−307 – −306|
|- Vikram Samvat||−243 – −242|
|- Shaka Samvat||N/A|
|- Kali Yuga||2801–2802|
|Iranian calendar||921 BP – 920 BP|
|Islamic calendar||949 BH – 948 BH|
|Minguo calendar||2211 before ROC|
|Seleucid era||12/13 AG|
|Thai solar calendar||243–244|
−173 or −554 or −1326
— to —
−172 or −553 or −1325
Year 300 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Corvus and Pansa (or, less frequently, year 454 Ab urbe condita). The denomination 300 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. B.C.E is the abbreviation for before the Common/Current/Christian Era (an alternative to Before Christ, abbreviated BC).
- Pilgrims travel to the healing temples of Asclepieion to be cured of their ills. After a ritual purification the followers bring offerings or sacrifices.
- Pyrrhus, the King of Epirus, is taken as a hostage to Egypt after the Battle of Ipsus and makes a diplomatic marriage with the princess Antigone, daughter of Ptolemy and Berenice.
- Ptolemy concludes an alliance with King Lysimachus of Thrace and gives him his daughter Arsinoe II in marriage.
- Seleucus founds the city of Antioch, some 20 miles up the Orontes River, naming it after his father.
- After the death of his wife Apama, Seleucus marries Stratonice, daughter of Demetrius Poliorcetes.
- The central texts of Jainism, the Jain scriptures, are recorded (approximate date).
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