|Millennium:||1st millennium BC|
|280 BC by topic|
|Gregorian calendar||280 BC|
|Ab urbe condita||474|
|Ancient Egypt era||XXXIII dynasty, 44|
|- Pharaoh||Ptolemy II Philadelphus, 4|
|Ancient Greek era||125th Olympiad (victor)¹|
|Balinese saka calendar||N/A|
|Chinese calendar||庚辰年 (Metal Dragon)|
2417 or 2357
— to —
辛巳年 (Metal Snake)
2418 or 2358
|Coptic calendar||−563 – −562|
|Ethiopian calendar||−287 – −286|
|- Vikram Samvat||−223 – −222|
|- Shaka Samvat||N/A|
|- Kali Yuga||2821–2822|
|Iranian calendar||901 BP – 900 BP|
|Islamic calendar||929 BH – 928 BH|
|Minguo calendar||2191 before ROC|
|Seleucid era||32/33 AG|
|Thai solar calendar||263–264|
−153 or −534 or −1306
— to —
−152 or −533 or −1305
Year 280 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Laevinus and Coruncanius (or, less frequently, year 474 Ab urbe condita). The denomination 280 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.
- Antiochus makes his eldest son, Seleucus, king in the east, but he proves to be incompetent.
- Antiochus is compelled to make peace with his father's murderer and King of Macedon, Ptolemy Keraunos, abandoning, for the time being, his plans to control Macedonia and Thrace.
- Nicomedes, King of Bithynia, is threatened with an invasion from Antiochus who has already made war upon his father, Zipoites. Antiochus actually invades Bithynia but withdraws again without risking a battle.
- Antiochus is unable to bring under his control the Persian dynasties that rule in Cappadocia.
- Antiochus is defeated by Egypt's Ptolemy II in the Damascene War.
- Pyrrhus makes an alliance with Ptolemy Keraunos, King of Macedon. This allows him to go to southern Italy with his army.
- The Achaean League is reformed by twelve towns in the northern Peloponnesus and will later grow to include non-Achaean cities. It has two generals, a federal council with proportional representation of members and an annual assembly of all free citizens. The League achieves a common coinage and foreign policy and the member cities pool their armed forces.
- Rhodes, rising in prosperity, becomes head of an Island League and helps to keep the peace and freedom of the Greek islands in the Aegean Sea.
- The Colossus of Rhodes is completed by the sculptor Chares of Lindos after twelve years' work. It becomes one of the seven wonders of the ancient world. The Colossus of Rhodes is a giant statue of the Greek god Helios. It stands 70 cubits tall, over 30 metres (100 feet), making it the tallest statue of the ancient world.
- Responding to an appeal from Tarentum, King Pyrrhus of Epirus uses his army of over 20,000 men against the Romans. In the Battle of Heraclea he defeats a Roman army led by consul Publius Valerius Laevinus. Pyrrhus's judicious use of his elephants plays a large part in his victory. Several tribes including the Lucani, Bruttii and the Messapians as well as the Greek cities of Crotone and Locri join Pyrrhus.
- Roman commander and statesman, Gaius Fabricius Luscinus, is sent to negotiate the ransom and exchange of prisoners. Pyrrhus is so impressed by Fabricius refusing to accept a bribe, that Pyrrhus releases the prisoners without the requirement for a ransom. Following his victory, Pyrrhus advances as far north as Latium.
- Aristarchus of Samos uses the size of the Earth's shadow on the Moon to estimate that the Moon's radius is one-third that of the Earth. He proposes for the first time a heliocentric view of the Solar System, but is ignored due to the lack of evidence of the Earth's motion.
- Philo of Byzantium, a Greek writer on mechanics (approximate date) (d. c. 220 BC)
- Han Fei, Chinese philosopher who has developed Xun Zi's philosophy (approximate date)
- Li Si, influential prime minister (or chancellor) of the feudal state and later of the dynasty of Qin (approximate date) (d. 208 BC)
- Herophilus, Alexandrian physician who has been an early performer of public dissections on human cadavers; often called the father of anatomy (b. c. 335 BC)
- Demetrius of Phaleron (or Demetrius Phalereus), Athenian orator, statesman, and philosopher, who has become prominent at the court of Ptolemy I, enjoying a high reputation as an orator (b. c. 350 BC)