October 1, 331 BC: Alexander the Great defeats the Persians at the Battle of Gaugamela.
Also called the Battle of Arbela, this clash between a twenty-five-year old Alexander the Great and Darius III, who would be the last king of the Achaemenid Empire, was third in a series of major battles between the young Conqueror and the forces of Persian Empire. The other two were the Battles of Granic River (334) and Issus (333). It is considered one of the most decisive battles in history by many, including Sir Edward Shepherd Creasy, who went so far as to say that “… the ancient Persian empire, which once subjugated all the nations of the earth, was defeated when Alexander had won his victory at Arbela.” You can read Creasy’s (very pro-Western) analysis of the battle here, chapter three. He compares the Western conquest of the East to the British Empire’s ” present mission is to break up the mental and moral stagnation of India and Cathay”.
The battle was fought on a flat plain, with around 47,000 troops in the Macedonian army and a contested amount (no more than 100,000, but certainly outnumbering Alexander’s forces) on the Persian side. Darius’s army was a diverse group, including warriors atop scythed chariots, thousands of Persian Immortals, and even war elephants, which impressed even Alexander himself, but they were poorly trained and equipped. The battle ended in a devastating victory for the Macedonians, and Darius fled in humiliating defeat before the battle had even been decided. The king was eventually murdered in 330, but Alexander, who had hoped to capture him alive, granted him a funeral at Persepolis after discovering the body. In 324, Alexander married Darius’s daughter Stateira II.
Despite having conquered the empire, Alexander (an admirer of the first Achaemenid king, Cyrus the Great) allowed many of the satraps to retain their positions; he also attempted to preserve Persian customs like proskynesis.