Pyrrhus was the son of Aeacides of Epirus and Phthia, and a second cousin of Alexander the Great. Prince of one of the Alexandrian successor states, Pyrrhus' childhood and youth went by in unquiet conditions. He was only two years old when his father was dethroned and the family took refuge with Glaukias, king of the Taulanti, one of the largest Illyrian tribes.
Later, the Epirotes called him back but he was dethroned again at the age of 17 when he left his kingdom to attend the wedding of Glaukias' son in Illyria. In the wars of the diadochi Pyrrhus fought beside his brother-in-law Demetrius I of Macedon on the losing side in the pivotal Battle of Ipsus (301 BC). Later, he was made a hostage of Ptolemy I Soter by a treaty between Ptolemy I and Demetrius. Pyrrhus married Ptolemy I's stepdaughter Antigone and in 297 BC, with Ptolemy I's aid, restored his kingdom of Epirus. Next he went to war against his former ally Demetrius. By 286 BC he had deposed his former brother-in-law and taken control over the kingdom of Macedon. Pyrrhus was driven out of Macedon by Lysimachus, his former ally, in 284 BC.
In 281 BC, the Greek city of Tarentum, in southern Italy, fell out with Rome and was faced with a Roman attack and certain defeat. Rome had already made itself into a major power, and was poised to subdue all the Greek cities in Magna Graecia. The Tarentines asked Pyrrhus to lead their war against the Romans.
Pyrrhus was encouraged to aid the Tarentines by the oracle of Delphi. His goals were not, however, selfless. He recognized the possibility of carving out an empire for himself in Italy. He made an alliance with Ptolem Ceraunus, King of Macedon and his most powerful neighbor, and arrived in Italy in 280 BC.
He entered Italy with an army consisting of 3,000 cavalry, 2,000 archers, 500 slingers, 20,000 infantry and 20 war elephants in a bid to subdue the Romans.
Due to his superior cavalry and his elephants he defeated the Romans, led by Consul Publius Valerius Laevinus, in the Battle of Heraclea in 280 BC. There are conflicting sources about casualties. Hieronymus of Cardia reports the Romans lost about 7,000 while Pyrrhus lost 3,000 soldiers, including many of his best. Dionysius gives a bloodier view of 15,000 Roman dead and 13,000 Greek. Several tribes including the Lucani, Bruttii, Messapians, and the Greek cities of Croton and Locri joined Pyrrhus. He then offered the Romans a peace treaty which was eventually rejected. Pyrrhus spent winter in Campania.
When Pyrrhus invaded Apulia (279 BC), the two armies met in the Battle of Asculum where Pyrrhus won a very costly victory. The consul Publius Decius Mus was the Roman commander, and his able force, though defeated, broke the back of Pyrrhus' Hellenistic army, and guaranteed the security of the city itself. The battle foreshadowed later Roman victories over more numerous and well armed successor state military forces and inspired the term "Pyrrhic victory", meaning a victory which comes at a crippling cost. At the end, the Romans had lost 6,000 men and Pyrrhus 3,500 but, while battered, his army was still a force to be reckoned with.
In 278 BC, Pyrrhus received two offers simultaneously. The Greek cities in Sicily asked him to come and drive out Carthage, which along with Rome was one of the two great powers of the Western Mediterranean. At the same time, the Macedonians, whose King Ceraunus had been killed by invading Gauls, asked Pyrrhus to ascend the throne of Macedon. Pyrrhus decided that Sicily offered him a greater opportunity, and transferred his army there.
Pyrrhus was proclaimed king of Sicily. He was already making plans for his son Helenus to inherit the kingdom of Sicily and his other son Alexander to be given Italy. In 277 Pyrrhus captured Eryx, the strongest Carthaginian fortress in Sicily. This prompted the rest of the Carthaginian-controlled cities to defect to Pyrrhus.
In 276 BC, Pyrrhus negotiated with the Carthaginians. Although they were inclined to come to terms with Pyrrhus, supply him money and send him ships once friendly relations were established, he demanded that Carthage abandon all of Sicily and make the Libyan Sea a boundary between themselves and the Greeks. Meanwhile he had begun to display despotic behavior towards the Sicilian Greeks and soon Sicilian opinion became inflamed against him. Though he defeated the Carthaginians in another battle, he was forced to abandon Sicily and return to Italy.
While Pyrrhus had been campaigning against the Carthaginians, the Romans rebuilt their army by calling up thousands of fresh recruits. When Pyrrhus returned from Sicily, he found himself vastly outnumbered against a superior Roman army. After the inconclusive Battle of Beneventum in 275 BC Pyrrhus decided to end his campaign in Italy and return to Epirus which resulted in the loss of all his Italian holdings.
Though his western campaign had taken a heavy toll on his army as well as his treasury Pyrrhus yet again went to war. Attacking King Antigonus II Gonatas he won an easy victory and seized the Macedonian throne.
In 272 BC, Cleonymus, a Spartan of royal blood who was hated among fellow Spartans, asked Pyrrhus to attack Sparta and place him in power. Pyrrhus agreed to the plan intending to win control of the Peloponnese for himself but unexpectedly strong resistance thwarted his assault on Sparta. He was immediately offered an opportunity to intervene in a civic dispute in Argos. Entering the city with his army by stealth, he found himself caught in a confused battle in the narrow city streets. During the confusion an old Argead woman watching from a rooftop threw a roofing tile which stunned him, allowing an Argive soldier to kill him (some reports claim he was poisoned by a servant).
While he was a mercurial and often restless leader, and not always a wise king, he was considered one of the greatest military commanders of his time. Plutarch records that Hannibal ranked Pyrrhus as either the greatest or the second greatest commander the world had seen (after Alexander the Great if the second version of the tradition is followed). Pyrrhus was also known to be very benevolent. As a general Pyrrhus' greatest political weaknesses were the failure to maintain focus and the failure to maintain a strong treasury at home (many of his soldiers were costly mercenaries).
His name is famous for the phrase "Pyrrhic victory" which refers to an exchange at the Battle of Asculum. In response to congratulations for winning a costly victory over the Romans, he is reported to have said: "One more such victory will undo me!" (In Greek: Αν έτι μίαν μάχην νικήσωμεν, απολώλαμεν.)
Pyrrhus wrote Memoirs and several books on the art of war. These have since been lost although Hannibal was influenced by them and they received praise from Cicero.