|Millennium:||1st millennium BC|
|Centuries:||4th century BC – 3rd century BC – 2nd century BC|
|Decades:||330s BC 320s BC 310s BC – 300s BC – 290s BC 280s BC 270s BC|
|Years:||303 BC 302 BC 301 BC – 300 BC – 299 BC 298 BC 297 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|
|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||2802–2803|
|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|
|Wikimedia Commons has media related to 300 BC.|
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.
- 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).
- In Pella (in Macedonia), the artist Gnosis makes a mosaic floor decoration called Stag Hunt and even signs it with "Gnosis made it". It is today preserved at the Archaeological museum in Pella.