The Macedonian Invasion of Anatolia was a short lived invasion of the Persian Empire, specifically in Anatolia, by Macedonian and Greek forces under the command of Alexander III of Macedon. The conflict began relatively calm, being prepared for by years by both Alexander and his father, Philip II.
After the assassination of Philip II, Alexander became king of Macedon and began a series of campaigns in Greece and the Balkans, to restore Macedonian hegemony over the Greek states, and to ensure that his border would be secured during an invasion in the east. In 335 BC, Alexander launched his invasion, crossing into Anatolia over the Hellespont with an army of about 37,000 Macedonian and Greek soldiers, transported on over one hundred triremes.
Initially Darius III was hesitant to mobilize Persian forces against Alexander, and one of his generals, Memnon of Rhodes, a Greek mercenary aligned with the Persians, instead advocated for the destruction of Persian lands in front of Alexander, so that his army would starve and he would be forced to retreat back to Greece, Scorched earth. Alexander continued to advance into Persian territory, and eventually Darius appointed Memnon the head of an army to meet Alexander on the battlefield, hoping that a confrontation would lead to his defeat.
At the Battle of the Granicus Alexander's forces met the Persians on the field of battle, and although initially successful, the Macedonians would be defeated when their leader Alexander was struck down and killed, causing a rout of the invading army, and the eventual retreat of the entire invading force. With Alexander dead, the forces of Macedon returned home, weary of further invasion in Persia in the future, and now in conflict over Alexander's succession.
Assassination of Philip II
When the other nations of Greece learned of Philip's death they entered into a state of rebellion against Alexander. This included Thebes, Athens, Thessaly, and the Thracian tribes to the north of Macedon, which sought to be freed of Macedonian influence. Alexander's advisers cautioned the king by recommending he use diplomacy to subdue the Greeks. This was ignored by Alexander, who mustered an army of 3000 Macedonian cavalry and rode south into Thessaly. The Thessalian army had garrisoned in the pass between Mount Olympus and Mount Ossa, and Alexander had his men ride over Mount Ossa to launch a surprise attack on the defending Greeks. When the Thessalian army awoke the next morning they found Alexander to their rear and surrendered, their cavalry joining Alexander's force as he rode down toward the Peloponnesus. Alexander rode on to Thermopylae, before heading south for Corinth, where he received the title of Hegemon. After crossing into the Peloponnesus the city of Athens sued for peace with Alexander. Alexander was appointed commander of the upcoming war with Persia, succeeding his father as commander of the Greek army.
With the majority of the Greek states now under Alexander's control, he embarked on a campaign in the Balkans to pacify the region and to ensure his border would be safeguarded during his invasion of Persia. With an army of 2000 heavy infantry, 8000 light infantry, and 3000 cavalry, Alexander first marched into Thrace, to deal with revolts from the native Illyrians and Triballi. Alexander's friend Langarus, of the Agriani, a Thracian tribe in the region, reinforced Alexander's forces further as he advanced into the rebellious territory. Alexander's forces marched onto Mount Haemus, where they engaged a Thracian garrison stationed on the mountainside. The defending Thracian army had constructed a defensive wall out of carts, which they intended to throw upon the Macedonians as they approached. Alexander ordered his heavy infantry to proceed up the hill, and when the carts were released, to either jump to the side or duck underneath the carts. At the same time the Macedonian archers opened fire upon the defender's position. With the hill clear to advance up, the Macedonian infantry proceeded toward the defensive positions causing the Thracians to rout.
As the battle was breaking out, King Syrmus of the Triballi had arrived with a large army intending to advance against the Macedonian rear. The Triballi were unable to penetrate the enemy lines and retreated to the gorge, before being drawn back out by Alexander's light infantry. As they proceeded back into the open battlefield the Triballi were crushed by Alexander's forces, leaving an estimated 3000 dead.
With the battle against the Thracians and Triballi over, the Macedonians marched to the Danube River, where they encountered the Getae tribe waiting on the opposite shore. Alexander's ships failed to enter the river, so instead Alexander's army constructed rafts out of their leather tents, transporting a force of 4000 infantry and 1500 cavalry across the river. The Getae army, numbering about 14,000 men in size, retreated after the Macedonian cavalry engaged them, leaving their town to be taken by the Macedonian army.
With Greece and the Balkans secured under the rule of Alexander, he set out on an expedition into Anatolia, the result of years of planning, first begun by his father Philip II. Alexander crossed the Hellespont into Anatolia, with the army of Macedon being transported by over one hundred triremes. This movement was initially ignored by the Persians, who were hesitant to act. For the first three months of Alexander's invasion he was not taken seriously by the Persians, and Darius refused to mount a serious offensive against him. Scorched earth tactics were proposed by Memnon of Rhodes, a Greek mercenary aligned with the Persians, advocating for the destruction of Persian lands in front of Alexander, so that his army would starve and he would be forced to retreat back to Greece, a Scorched earth policy. But the noble satraps of Anatolia refused to pillage their own land. Alexander continued to advance into Persian territory, and eventually Darius appointed Memnon the head of an army to meet Alexander on the battlefield, hoping that a confrontation would lead to his defeat.
Battle of the Granicus
In May, Alexander's forces met Memnon on the battlefield, at the Granicus River in northwestern Anatolia, near the site of ancient Troy. During the battle, Alexander would be struck down and killed by a Persian commander, ending the campaign altogether, and forced Macedonian leadership and troops to return to Greece.