Alexander the Great
The Macedonian king who destroyed the Persian Empire before he was 30 and left a Greek-speaking world stretching from Egypt to Afghanistan.
In eleven years Alexander III of Macedon marched an army from northern Greece to the Punjab, destroyed the Persian Empire, and never lost a battle. He was 32 when he died in Babylon in June 323 BC. His empire fell apart almost immediately. The Greek-speaking world he created lasted three centuries, and Rome inherited it.
His father did the hard part. Philip II turned Macedon from a backwater into the strongest military power in Greece, built the long-pike phalanx and a professional standing army, and had already ordered the invasion of Persia when he was assassinated in 336 BC. Alexander was 20. He spent two years crushing revolts at home, then crossed into Asia in 334 with about 40,000 men and very little money.
Eleven years
He won at the Granicus in 334, then at Issus in 333, where Darius III fled the field and left his own mother, wife, and children behind. Instead of chasing him, Alexander turned south to take the coastline, so the Persian fleet would have nowhere to dock. Tyre held out for seven months and was destroyed for it. Egypt surrendered without a fight, and he founded Alexandria there in 331.
Gaugamela, in October 331, ended the empire. Alexander drove a cavalry wedge into a gap that opened in the Persian line, Darius ran again, and Babylon, Susa, and Persepolis fell in sequence. Persepolis, the Persian ceremonial capital, was burned. In 330 Darius was murdered by one of his own satraps, which left Alexander as the only man with a claim to the throne.
The rest was harder than the conquest. Three years of guerrilla warfare in Bactria and Sogdiana, then India, where he beat King Porus and his war elephants at the Hydaspes in 326. At the next river the army refused to go on. He turned back, marched a large part of it through the Gedrosian desert and lost thousands to thirst and heat, and reached Babylon in 323. He died there of a fever, at 32, having named no successor.
Becoming Persian
What his officers could not forgive was what he did with the victory. Alexander left Persian administrators in their jobs, adopted parts of Persian court dress, and tried to introduce proskynesis, the bow Persians performed before their king. Greeks bowed only to gods. He married Roxana, a Bactrian noblewoman, and at Susa in 324 he married a daughter of Darius and had roughly eighty of his officers marry Persian women in the same ceremony. He put 30,000 Persian youths through Macedonian training.
His men read all of this as their king going native. He killed his friend Cleitus in a drunken argument about it. His court historian Callisthenes, who was Aristotle's nephew, was arrested over the bowing and died in custody. Whether Alexander genuinely believed in a merged ruling class or simply understood that 40,000 Macedonians could not hold Persia on their own, it was the first serious attempt to run a multiethnic empire with a mixed elite.
What survived
Within two years of his death his generals were at war with each other. After forty years of fighting, three dynasties held the pieces: the Ptolemies in Egypt, the Seleucids across Asia, the Antigonids in Macedon. Greek became the working language of government and trade from the Adriatic to the Indus. Alexandria grew into the largest city in the Mediterranean and the site of its greatest library. Greek kings ruled in Afghanistan for two centuries, and their coins carry Greek on one face and Indian scripts on the other.
Rome grew up next to that world rather than a Persian one, which is why educated Romans spoke Greek and why Roman commanders kept measuring themselves against him. Caesar is supposed to have wept in front of a statue of Alexander, having reached his thirties with nothing comparable to show. Napoleon took a small army of scholars to Egypt in conscious imitation. The pattern of the young conqueror who wins everything and leaves nothing that outlives him starts here.