At one point in antiquity, the Achaemenid Persian Empire was the largest empire the world had ever seen, but aside from its role in the Greco-Persian Wars and its collapse at the hands of Alexander the Great, it has been mostly overlooked. When it has been studied, the historical sources have mostly been Greek, the very people the Persians sought to conquer. Needless to say, their versions were biased, and attitudes about the Persians were only exacerbated by Alexander the Great and his biographers, who maintained a fiery hatred toward Xerxes I of Persia due to his burning of Athens.

Of course, far more is known about Alexander the Great and his military accomplishments, the most important of which was bringing about the demise of the Persian Empire. Ever since the famous Persian invasions that had been repelled by the Athenians at Marathon and then by the Spartans at Thermopylae and Plataea, Greece and Persia had been at odds. For the past few years they had enjoyed an uneasy peace, but that peace was shattered when, in 334 BCE, Alexander crossed the Hellespont into Persia. He brought with him an army of 50,000 infantry, 6,000 cavalry and a navy of over 100 ships, a mixed force of Macedonians, Greeks, Thracians and Illyrians, all chosen for their specific strengths (the Thessalians, for example, were famous cavalrymen). He was still just 22.

Darius III, king of Persia at the time of Alexander’s invasion, was no tactical genius, but he was an intelligent and persistent enemy who had been handed the throne just before the arrival of the indomitable Alexander. His misfortune was to face an enemy at the forefront of military innovation and flexibility, a fighting force that he was not equipped to handle, and the unconquerable will of the Macedonian army, fueled by devotion to their daring and charismatic king.

When Alexander crossed the Hellespont in 334 BCE, his first encounter with Persian forces took place along the Granicus River. The Persian commanders had met at the city of Zeleia along with Memnon of Rhodes, the leader of their Greek mercenary forces, and Memnon advised the Persians not to fight Alexander head on. Since the Persian forces were slightly outnumbered for the battle, Memnon advised that the Persians should scorch the nearby lands and make travel and supplying the army difficult for Alexander.

Ultimately, however, the Persians did not trust the Greek commander and were unwilling to destroy their own lands. It’s quite likely they thought that the young inexperienced king at the head of a Greek army would not be too difficult to defeat, so they instead decided to draw Alexander into a defensive position of their own choosing. Against a lesser general, their strategy might have worked well, but at the Battle of the Granicus River, the Persians would learn that Alexander was no typical military leader.

What happened there set the tone for the rest of Alexander’s campaign against the Persians, including at the legendary Battle of Issus, but over 2,000 years after the Battle of the Granicus River was fought, there are still a lot of lingering questions surrounding it. Though it’s frequently grouped with Alexander’s other three major military encounters (the Battle of Issus, the Battle of Gaugamela, and the Battle of Hydaspes), the ancient sources lack the detailed information about the battle dispositions and the actual activities of the battle that characterize their accounts of the other three.

The Battle of the Granicus River: The History of Alexander the Great’s First Major Battle Against the Achaemenid Persian Empire looks at one of antiquity’s most important battle.