In spring 334 BCE, Alexander led his army across the Hellespont (Dardanelles), beginning the direct Macedonian invasion of Achaemenid imperial territory and initiating the campaign that would dismantle Persian power in the west.
Alexander’s first major victory over Persian satrapal forces at the Granicus River secured a foothold in Asia Minor and encouraged further defections and surrender of key cities to Macedonian rule.
The hard-fought siege at Halicarnassus (Caria) removed a major Persian strongpoint in southwest Anatolia, helping Alexander reduce Persian leverage along the Aegean and secure lines of movement for the inland advance.
At Issus, Alexander defeated King Darius III’s field army in a decisive engagement, forcing Darius to flee and leaving members of the royal family in Macedonian hands—an outcome that severely weakened Achaemenid political authority.
The prolonged siege of the island city of Tyre ended with Macedonian victory, eliminating a key Persian-aligned naval base and enabling Alexander to complete control of the Levantine coast before moving south toward Egypt and then east again.
At Gaugamela (also called Arbela), Alexander won the decisive battle against Darius III, effectively ending organized Achaemenid resistance in the west and opening the core imperial lands to Macedonian occupation.
Following Gaugamela, Babylon—one of the empire’s greatest cities—submitted to Alexander, providing him a major administrative and symbolic center and signaling the rapid collapse of Persian control across Mesopotamia.
Susa, an Achaemenid capital and critical treasury center, surrendered without a fight; Alexander’s acquisition of its wealth strengthened his capacity to pay troops and govern the expanding conquest.
In winter 330 BCE, Persian forces attempted to stop Alexander at the narrow pass known as the Persian Gate; Alexander’s victory overcame one of the last effective geographic defenses before Persepolis.
Alexander entered Persepolis, the ceremonial heart of Achaemenid kingship, and seized its palaces and immense treasure—an irreversible blow to the dynasty’s prestige and to any claim of continued imperial continuity.
After the capture and looting of Persepolis, the royal palace complex was set on fire—an event remembered in ancient sources and later tradition as a powerful symbolic act marking the end of the old imperial order.
As Alexander pursued him toward eastern satrapies, Darius III was deposed and killed by conspirators (commonly associated with Bessus). His death removed the last reigning Achaemenid “King of Kings,” accelerating the transition of imperial claims to Alexander.
Alexander the Great's Conquest of the Achaemenid Empire (334–330 BCE)
