First of the three battles of Alexander the Great's Asian campaign (the second being the Battle of Issus and the last the Battle of Gaugamela). Fought against the Persian Forces in May/June 334 BC in the valley of the River Granicus, approximately 100km from the site of the ancient city of Troy.
Background: After quashing the Theban revolt, Alexander went north to his native Macedonia. Plutarch recounts a visit the oracle at Delphi on the way. As it was an inauspicious day, when it is forbidden for the oracle to give a reply, the prophetess would not speak to those he sent for her. Nevertheless he had her summoned and when she explained this to him he went up to her himself to the shrine. Overcome by his persistence, she exclaimed, "You are invincible my son!" and Alexander declared that this was prophecy enough for him. In Macedonia he offered thanks to Olympian Zeus. During the ceremonies a report came in that the statue of Orpheus, had been constantly sweating - a phenomenon interpreted as a bad omen by many of the seers. However, one of them, Aristander of Telmissus, told Alexander that it was no cause for alarm as it merely signified that the writers of odes and epics had hard working coming to celebrate Alexander's exploits in verse and song.
At the start of the next campaigning season Alexander left Antipater in charge of affairs in Macedonia and Greece and set out for the Hellespont, the major crossing between Asia Minor and mainland Greece.
His forces were said to number 30,000 infantry and over 5,000 cavalry, according to Arrian. Diodorus confirms these figures. However modern estimates are larger as an advance force of 10,000 had already crossed into Asia Minor. The cavalry included as many Thessalians as Macedonians and the other Greek states, members of the League Of Corinth, contributed about 7,000 infantry and 600 cavalry. Besides the operational troops, the expedition included reconnaissance staff and many other specialists including geographers, historians, astronomers, seers and zoologists.
Parmenio was entrusted with the task of getting the forces across the Hellespont and this was achieved by use of some 160 triremes and a large number of merchant vessels. Once ashore, the army travelled inland to Troy. One account says that Alexander laid a wreath on the tomb of Achilles, whilst his dearest friend and companion since boyhood Hephaestion laid one on the tomb of Patroclus : a symbolic gesture comparing their relationship and greatness with that of two of the chief heroes of Homer's Iliad. Sacrifices were also made to Athene, patron goddess of Troy. He continued on his route inland, sending a party under Panegorus to take over the town of Priapus, which surrendered to him.
The Persian forces were under the command of number of governors and generals: Arsames, Rheomithres, Petines and Niphates in association with Spithridates, satrap of Lydia and Ionia, and Arsites, the governor of norther Phrygia. They had taken up a position near the town of Zeleia with the Persian cavalry and Greek mercenary troops. On receiving the report that Alexander had crossed into Asia they met to discuss the situation. Memnon of Rhodes advised against risking an engagement as the Macedonian infantry were greatly superior in numbers and Alexander was present whilst Darius, King of Persia, was not. He advocated a scorched earth policy to prevent Alexander, through lack of supplies, from remaining in the country. These proposals were rejected, perhaps motivated partially by jealousy that Memnon, a foreigner had risen to a position in the ruling class of Persia through marriage.
Meanwhile Alexander was advancing in battle order upon the river Granicus. His infantry was massed in two groups, both wings protected by the cavalry, while all transport had orders to follow in the rear. Many of the officers thought that Alexander should observer the old Macedonian tradition and refrain from engaging in battle in the month of Daesius (May-June, the time for the gathering of the harvest). Parmenio was also opposed to an engagement, reasoning that the Persian forces would probably withdraw overnight, as they were smaller, leaving Alexander free to cross the river. He also stated that a failure at this early stage of the campaign would be highly detrimental to Alexander's success in the long run. Alexander swept aside these concerns, telling Parmenio that "I should be ashamed of myself if a little trickle of water like this were too much for us to cross without further preparation, when I had no difficulty in crossing the Hellespont. Such hesitancy would be unworthy of the fighting fame of our people and of my own promptitude in the face of danger." In fact, nothing could have suited Alexander better than the Persian deicision to fight. He realized the moral effect a victory would have on the Greek cities of Asia Minor, and wished the Persian commanders to have no excuses for what he regarded as their certain defeat. This rejection of Parmenio's advice is the first of a number of such incidents and many modern historians see it as an attempt by Alexander's historian and official propagandist Callisthenes to lessen the odium of Parmenio's murder by denigrating the old general.
The Battle: Alexander sent Parmenio to take command of the left wing, and himself moved to take command of the right. Philotas, Parmenio's son, was leading the Companion Cavalry, the archers and the Agriane spearman on the right. The Guards battallions were commanded by Nicanor, Parmenio's son, Pardiccas, Coenus and Philip, in that order from right to left. The advance position on the left wing was held by the Thessalian cavalry, supported by the Allied Cavalry and the Thracian Cavalry. Immediately to their right was the infantry phalanx with batallions under Craterus, Melager and Philip. The Persians had about 20,000 cavalry and nearly the same number of Greek mercenaries. They took up a position along the steep bank of the river with the cavalry to the front - a serious military blunder. Such a position deprived the cavalry of the opportunity the charge and the infantry of the chance to fight untill it was too late. They massed their squadrons directly opposite to Alexander.
Alexander was always unmistakable on the battlefield, with his magnificent armour, shield salvaged from Troy, and white plume affixed to his helmet, and his accompanying bodyguards. Alexander ordered the scouts under Amyntas to cross first, under heavy fire, obliquely to prevent the strong current from sweeping them away and also to prevent a flank attack as the emerged from the water. A hand-to-hand struggle developed as the Macedonian mounted troops tried to force themselves up from the steep bank of the river, with the Persians doing their utmost to prevent them. Alexander's men, heavily outnumbered as there were, suffered severely.
Many of these Macedonian troops died, and those who didn't fell back upon Alexander, who was now on his way across, at the head of the army's right wing. Round him a violent struggle developed while the rest of the body of the army crossed over the river with relative ease. Arrian says "It was a cavalry battle with infantry tactics: horse against horse, man against man, locked together..."
The experience of strength of numbers of Alexander's forces soon swayed the battle in their favour and their long cornel-wood spears were more effective than the throwing lances of the Persians. In the midst of the battle Alexander, armed with a fresh spear, caught sight of Darius' nephew Mithridates riding in with a squadron of cavalry in a wedge formation. Alexander galloped out in front of his men , struck Mithridates in the face with his spear, and hurled him to the ground. One of Mithridates' fellow commanders, Rhoesaces, sliced through Alexander's helmet with a scimitar and Alexander turned and speared him through his cuirass into his breast, killing him . Another commander, Spithridates, had his scimitar raised, ready to slice Alexander through from behind, but Cleitus the Black, commander of the Royal Squadron of Companion Cavalry, was upon him and severed his arm through his shoulder. Plutarch gives a very different account of this incident, but Arrian's military accounts tend to be more accurate due to his use of primary sources such as Ptolemy and Aristobulus. Meanwhile Alexander's party were being steadily reinforced by the mounted troops as one after another the succeeded in getting out of the river and joining him. The Persian army was now in a bad way: once the centre failed to hold, both cavalry wings had broke to flee and the rout was complete.
About 1,000 were killed, more could have been but Alexander checked their pursuit in order to turn his attention to the foreign mercenaries, who had remained in their original position, startled by the suddenness of the rout. Alexander ordered a combined assault of infantry and cavalry, surrounded them and butchered almost all of them, taking 2,000 Greek prisoners, who were sent back to Macedonia to work in the quarries for contravening the order the resolution of the Corinthian League by fighting against their countrymen.
Outcome: The Persians had lost some 20,000 infantry and 5,000 cavalry whilst the figures given for Macedonian losses: sixty mounted troops and thirty cavalrymen are suspiciously low, given the resistance they must have encountred from the desperate mercenaries. Alexander ordered that all the Macedonian dead were buried with their arms and equipment on the day of the battle, and their parents and children were granted immunity from local taxes. Statues were struck in bronze of the 25 dead Cavalry Companions. Alexander also showed deep concern for the wounded, visiting them all and willingly listening to their exaggerted stories of their part in the battle. He also gave rights of burial to Persian commanders and the Greek mercenaries. As an offering to the goddess Athena, he sent 300 suits of Persian armour to Athens. This was clearly an act of propaganda, designed to ensure the further cooperation of Athens and the other polis with him.
Alexander's decisive victory at the Granicus brought a substantial and immediate change in his situation. The city of Sardis, which was the principal seat of Persian power on the Asiatic seaboard, surrendered to him at once, as did much of the rest of the region, no doubt swayed by his policy of supporting the democratic regimes in these cities in Asia Minor, due not due any preference of his own for democracy, but simply because the Persians had supported oligarchies. Democracy was also restored in Ephesus. Miletus however, did not capitulate and was the scene of a protracted siege.
Arrian - The Campaigns of Alexander
Plutarch - Age of Alexander
Oxford Classical Dictionary