|Millennium:||1st millennium BC|
|279 BC by topic|
|Gregorian calendar||279 BC|
|Ab urbe condita||475|
|Ancient Egypt era||XXXIII dynasty, 45|
|- Pharaoh||Ptolemy II Philadelphus, 5|
|Ancient Greek era||125th Olympiad, year 2|
|Balinese saka calendar||N/A|
|Chinese calendar||辛巳年 (Metal Snake)|
2418 or 2358
— to —
壬午年 (Water Horse)
2419 or 2359
|Coptic calendar||−562 – −561|
|Ethiopian calendar||−286 – −285|
|- Vikram Samvat||−222 – −221|
|- Shaka Samvat||N/A|
|- Kali Yuga||2822–2823|
|Iranian calendar||900 BP – 899 BP|
|Islamic calendar||928 BH – 927 BH|
|Minguo calendar||2190 before ROC|
|Seleucid era||33/34 AG|
|Thai solar calendar||264–265|
−152 or −533 or −1305
— to —
−151 or −532 or −1304
Year 279 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Publius Sulpicius Saverrio and Publius Decius Mus (or, less frequently, year 475 Ab urbe condita). The denomination 279 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 many years.
- An army of Gauls under Brennus invade Greece. A section of the army, commanded by Bolgios, crushes a Macedonian army led by Ptolemy Keraunos, who is killed in the battle. At the narrow pass of Thermopylae, on the east coast of central Greece, Brennus' forces suffer heavy losses while trying to break through the Greek defence comprising the Phocians and the Aetolians. Eventually Brennus finds a way around the pass but the Greeks escape by sea. Brennus pushes on to Delphi where he is defeated and forced to retreat, after which he dies of wounds sustained in the battle. His army falls back to the river Spercheios where it is routed by Thessalians and Malians. Some of the survivors settle in a part of Asia Minor that will eventually be called Galatia, while some settle in Thrace, founding a short-lived city-state named Tylis.
- With the death of Ptolemy Keraunos, the previous King of Macedonia, Antipater II becomes king again. However, his new reign lasts only few months before he is killed by his cousin Sosthenes who becomes the new King of Macedonia.
- The Phocians are readmitted into the Amphictyonic League after they have joined in the defence of Delphi against the Gauls.
- The Carthaginians and the Romans agree to support each other against a common foe. The Carthaginians give Rome money and ships in their fight against Pyrrhus, the king of Epirus.
- Pyrrhus realizes that he cannot capture Rome and suggests peace terms to the Romans. Pyrrhus sends his chief advisor, Cineas, to Rome to negotiate a peace. Cineas demands that the Romans halt their aggression against the Greeks of southern Italy and restore the lands the Romans have taken from the Bruttii, the Apulians, and the Samnites. The Romans reject his demands, largely at the instigation of the former Roman censor, Appius Claudius Caecus.
- In renewed fighting, Pyrrhus of Epirus, leading the combined Tarantine, Oscan, Samnite, and Greek forces, wins a 'Pyrrhic victory' against the Romans led by consul Publius Decius Mus at the Battle of Asculum, called such because his victory comes at a great cost to his own forces. Pyrrhus is reported to have said afterwards, "One more victory against the Romans and we shall be utterly ruined!" Disheartened, Pyrrhus retires to Tarentum and sends Cineas to make renewed peace overtures to Rome. These talks are inconclusive.
- The aggression of Ptolemy II of Egypt continues to cause friction with Antiochus as he takes Miletus in south-western Asia Minor from him.
- Scordisci Celts found a city called Singidon (Roman Singidunum) which is today the Serbian city of Belgrade.
- Ptolemy Keraunos, king of Macedonia from 281 to 279 BC
- Brennus, leader of the army of Gauls who in 279 BC invaded Macedonia and northern Greece