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 Dominicalendar 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.
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.
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.