280s BC

Sicily

• The tyrant of Syracuse, Agathocles, dies after restoring the Syracusan democracy on his death bed by stating that he does not want his sons to succeed him as king. However, the resulting dissension among his family about the succession leads to a renewal of Carthaginian power in Sicily.

China

• General Sima Cuo of the State of Qin attacks the State of Wei, recaptures the city of Yuan and captures the cities of Heyong and Jueqiao.

Greece

• The Macedonian King, Demetrius Poliorcetes, faces a combined attack from Lysimachus and Phyrrhus, king of Epirus, after Seleucus, Ptolemy and Lysimachus form a coalition to block plans by Demetrius to invade Asia Minor.

Ptolemy's fleet appears off Greece, inciting the cities to revolt.

• Athens revolts and Demetrius besieges the city. Pyrrhus takes Thessaly and the western half of Macedonia and, with the assistance of Ptolemy's fleet, relieves Athens from Demetrius' siege.
• After the Egyptian fleet participates decisively in the liberation of Athens from Macedonian occupation, Ptolemy obtains the protectorate over the League of Islanders, which includes most of the Greek islands in the Aegean Sea. Egypt's maritime supremacy in the Mediterranean in the ensuing decades is based on this alliance.

Sicily

• Following the death of Agathocles, some of his disbanded mercenaries seize Messana in northeast Sicily and set up a society, calling themselves Mamertines (Sons of Mars). The city becomes a base from which they will ravage the Sicilian countryside.

Sri Lanka

• The Jaya Sri Maha Bodhi Sacred Fig tree is planted at Anuradhapura, Sri Lanka. This is the earliest known planting date for any planted tree still surviving.

China

• King Zhao of Qin and King Min of Qi take the title "Di", (帝 literally emperor), of the west and east respectively. They swear a covenant and begin planning an attack on the State of Zhao.
• Qi conquers the State of Song.

Roman Republic

• A new law, Lex Hortensia, gives much greater power to the Concilium Plebis (Plebeian Council) compared to the Senate. This law is passed following a threat from plebeian soldiers to secede. In the face of this threat, the Senate yields to plebeian concerns over their lack of political power and over their level of debt to the aristocracy. The law is named after Quintus Hortensius, a plebeian, who is made dictator to settle the controversy.
• With the Lex Hortensia in place, in theory the political distinctions in Rome between the patricians and the plebeians disappear. However, in practice, the coalition of leading plebeian families keep control which means that the patricians are able to largely nullify the power of the assemblies. So Roman government continues to be oligarchic in character.

Greece

• The Macedonians resent the extravagance and arrogance of Demetrius Poliorcetes and are not prepared to fight a difficult campaign for him. When Pyrrhus of Epirus takes the Macedonian city of Verroia, Demetrius' army promptly deserts and goes over to Pyrrhus' side as he is much admired by the Macedonians for his bravery. At this change of fortune, Phila, the mother of Antigonus, kills herself with poison.
• Demetrius besieges Athens without success. He leaves Antigonus in charge of the war in Greece, assembles all his ships and embarks with his troops to attack Caria and Lydia, provinces in Asia Minor controlled by Lysimachus.
• Agathocles is sent by his father Lysimachus against Demetrius. Agathocles defeats Demetrius and drives him out of his father's provinces.
• Pyrrhus is proclaimed King of Macedonia.

Greece

• As Demetrius Poliorcetes and his army are chased across Asia Minor to the Taurus Mountains by the armies of Lysimachus and Seleucus, in Greece his son Antigonus meets with success. Ptolemy's fleet is driven off and Athens surrenders to Antigonus.
• After allowing Pyrrhus of Epirus to remain in possession of Macedonia with the title of king, he is expelled by Lysimachus who declares himself its king in the place of Pyrrhus.

Roman Republic

• The new law, Lex Aquilia, is enacted. This is a Roman law which provides compensation to the owners of property injured as a result of someone's fault.

China

• General Sima Cuo of the State of Qin attacks the Henei area of the State of Wei. Wei responds by handing over the major city of Anyi.

Egypt

• June 26 – Egypt's Ptolemy I Soter abdicates. He is succeeded by his youngest son by his wife Berenice, Ptolemy II Philadelphus, who has been co-regent for three years.
• A 110 metre tall lighthouse on the island of Pharos in Alexandria's harbour is completed and serves as a landmark for ships in the eastern Mediterranean. Built by Sostratus of Cnidus for Ptolemy II of Egypt, it is one of the seven wonders of the ancient world. It is a technological triumph and is the archetype of all lighthouses since. A broad spiral ramp leads to the top, where a fire burns at night.

Seleucid Empire

• Demetrius Poliorcetes is deserted by his troops and surrenders to Seleucus at Cilicia, where Seleucus keeps him a prisoner.

China

• The success of Qi has frightened the other states. Under the leadership of Lord Mengchang, who has been exiled in Wei, Qin, Zhao, Han and Yan form an alliance. Yan had normally been a relatively weak ally of Qi and Qi feared little from this quarter. Yan's onslaught under general Yue Yi comes as a devastating surprise. Simultaneously, the other allies attack from the west. Chu declares itself an ally of Qi but contents itself with annexing some territory to its north. Qi's armies are destroyed while the territory of Qi is reduced to the two cities of Ju and Jimo. King Min himself is later captured and executed by his own followers.

Roman Republic

• The Gallic tribe called the Senones, who have settled on the Adriatic coast north of Picenum, attack Arretium in Etruria. While attempting to relieve this allied city, the Romans under the command of Lucius Caecilius Metellus Denter suffer a costly defeat in the Battle of Arretium. Aroused by this disaster, a Roman army under Manius Curius Dentatus invades the Senones' territory, defeating them and driving them out of the Italian peninsula.

Asia Minor

• Ptolemy I's eldest (legitimate) son, Ptolemy Keraunos, whose mother, Eurydice, the daughter of Antipater, had been repudiated by the new King Ptolemy II, flees Egypt to the court of Lysimachus, the king of Thrace, Macedon and Asia Minor.
• Lysimachus' wife, Arsinoe, being keen to gain the succession to the kingdom of Thrace for her sons in preference to Agathocles (the eldest son of Lysimachus), intrigues against him with the help of her brother Ptolemy Keraunos. They accuse him of conspiring with Seleucus to seize the throne, and Agathocles is put to death. This atrocious deed by Lysimachus and his family arouses great indignation. Many of the cities in Asia Minor revolt and some of his most trusted friends desert him.
• Agathocles' widow Lysandra flees with their children and with Alexander, Agathocles' brother, to the court of Seleucus, who at once invades Lysimachus' territory in Asia Minor.

Culture

• The Ptolemaic court appoints Zenodotus of Ephesus as first Director of the Library of Alexandria.

Greece

• Following Demetrius Poliorcetes' death in captivity as a prisoner of Seleucus, his son Antigonus assumes the title of King of Macedonia, though in name only, as King Lysimachus of Thrace is in control of Macedonia. Demetrius' remains are given to Antigonus and he is honoured with a grand funeral in Corinth. After this, Demetrius is interred in the town of Demetrias which he had founded.

Roman Republic

• Consuls: Publius Cornelius Dolabella and Gnaeus Domitius Calvinus Maximus.
• At the Battle of Lake Vadimo, Roman forces finally quell the allied Etruscans and Gauls. The Roman army is led by consul Publius Cornelius Dolabella. Rome is at last undisputed master of northern and central Italy.

Egypt

• The canal from the Nile River to the Red Sea, initially started but not completed by the Egyptian pharaoh Necho II and repaired by the Persian king Darius I, is again repaired and made operational by Ptolemy II.
• Ptolemy II enlarges the library at Alexandria and appoints the grammarian Zenodotus to collect and edit all the Greek poets.

China

• General Lian Po of the State of Zhou defeats an army of the State of Qi and captures the city of Yangqin.

Asia Minor

• The city of Pergamum in Asia Minor ends its allegiance to Lysimachus. Its ruler, Philetaerus, transfers his allegiance, as well as the important fortress of Pergamon and his treasury, to Seleucus, who allows him a far larger measure of independence than he had hitherto enjoyed.

Roman Republic

• The Battle of Populonia is fought between Rome and the Etruscans. The Romans are victorious and, as a result, the Etruscan threat to Rome is sharply diminished.
• The Magna Graecia city of Thurii appeals to Rome for help against the native Italian tribes. Though the Roman Senate hesitates, the plebeian Assembly decides to respond. Thurii is saved, but Tarentum, jealous of Rome's interference, attacks and sinks some Roman ships entering its harbour. Roman envoys, sent to protest, are mistreated.
• Rome declares war on Tarentum. King Pyrrhus of Epirus declares his willingness to come to the aid of Tarentum. Tarentum also looks for support from the Samnites and other Italian tribes in southern Italy.

Egypt

• Arsinoe, daughter of Lysimachus, king of Thrace, marries Ptolemy II of Egypt as part of the alliance between Thrace and Egypt against Seleucus.

Asia Minor

• The Battle of Corupedium in Lydia is the last battle of the Diadochi, the rival successors to Alexander the Great. It is fought between the armies of Lysimachus, King of Thrace, Macedonia, Western Anatolia and Seleucus, ruler of Eastern Anatolia, Syria, Phoenicia, Judea, Babylonia and Iran. Seleucus kills Lysimachus during the battle.
• Following the Battle of Corupedium, Lysimachus's widow, Arsinoe, flees to Cassandrea, a city in northern Greece, where she marries her half-brother Ptolemy Keraunos. This proves to be a serious misjudgement, as Ptolemy Keraunus promptly kills two of her sons, though the third is able to escape. Arsinoe flees again, this time to Alexandria in Egypt.

Greece

• Seleucus takes over Thrace and then tries to seize Macedonia. However, he falls into a trap near Lysimachia, Thrace, set by Ptolemy Keraunos, one of the sons of Ptolemy I and Arsinoe II's half brother, who murders Seleucus and takes Macedonia for himself.
• Cineas, a Thessalian serving as chief adviser to King Pyrrhus of Epirus, after visiting Rome attempts, without success, to dissuade Pyrrhus from invading southern Italy.

Seleucid Empire

• Seleucus is succeeded as ruler of the Seleucid Empire by Antiochus, who was already king of the Syrian part of the empire. He is immediately beset by revolts in Syria (probably instigated by Ptolemy II of Egypt) and by independence movements in northern Anatolia.
• Although he has only a few bases in Greece, Antigonus II Gonatas lays claim to Macedonia. His claim is disputed by Antiochus I.

Seleucid Empire

• 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.

Greece

• 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. A giant statue of the Greek god Helios, it is the last completed of the seven wonders of the ancient world. It stands 70 cubits tall (over 30 metres or 100 feet), making it the tallest statue of the ancient world.

Roman Republic

• 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 of a ransom. Following his victory, Pyrrhus advances as far north as Latium.

China

• General Sima Cuo of the State of Qin attacks the State of Chu, conquering the western region of Qianzhong by marching through the region of Bashu. This conquest makes it easier for future Qin armies to invade Chu.
• General Bai Qi of Qin attacks the State of Zhou and captures the city of Guanglang.

Astronomy

• 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.