King Philip II of Macedonia had conceived a plan to attack the Persian Achaemenid Empire, which was in disarray after the murder of its king, Artaxerxes, in 338 BCE. In the spring of 336 BCE he sent ahead an advance force to seize a bridgehead on the Asian side of the Hellespont, the modern Sea of Marmara. Operations abruptly halted when Phillip II was murdered in the autumn of 336 BCE. His son, Alexander III, eliminated all possible rivals and assumed the kingship of Macedonia and the long planned campaign into Asia. A new King of Kings, Darius III, had emerged out of the chaos of the Achaemenid Empire in 336 BCE and had defeated the Macedonian advance force. Meanwhile, Alexander put down rebellions in Greece and, in the spring of 334 BCE, marched eastward with an army of 37,000. He crossed the Hellespont, meeting the Persian army of 40,000 under the command of Arsites, Satrap of Hellespontine Phrygia, which was deployed on the eastern bank of the River Granicus. The battle began with a Macedonian advance, which met firm resistance and was pushed back. Alexander and the Companions, the elite cavalry of the Macedonian army, attacked the Persian left flank, making gradual progress. The main body of the Macedonian army then renewed its attack, driving the Persians and their mercenaries from the battlefield, with around 6,000 lost. The Macedonians lost less than 200 men and now held the initiative in Asia Minor.
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