Over the last 2,000 years, ambitious men have dreamed of forging vast empires and attaining eternal glory in battle, but of all the conquerors who took steps toward such dreams, none were ever as successful as antiquity’s first great conqueror. Leaders of the 20th century hoped to rival Napoleon’s accomplishments, while Napoleon aimed to emulate the accomplishments of Julius Caesar. But Caesar himself found inspiration in Alexander the Great (356-323 BCE), the Macedonian king who managed to stretch an empire from Greece to the Himalayas in Asia by the age of 30. It took less than 15 years for Alexander to conquer much of the known world.

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. The Macedonians targeted many of his building projects after their capture of Persepolis, and they pushed an even bleaker picture of the king, one of an idle, indolent, cowardly, and corrupt ruler. It was not until excavations in the region during the 20th century that many of the relics, reliefs, and clay tablets that offer so much information about Persian life could be studied for the first time. Through archaeological remains, ancient texts, and work by a new generation of historians, a picture can today be built of this remarkable civilization and their most famous leaders.

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.

After the Battle of the Granicus River, the Persian king would personally face Alexander twice, once at the Battle of Issus and again at the Battle of Gaugamela, and the battles would help decide the fate of his empire and the fate of the Western world. In the wake of the Battle of Gaugamela, many historians believe that Alexander had already nominally conquered Persia. Alexander must have known he had vanquished his conquest's biggest obstacles, but for him, the war would not be won until Darius had been captured or killed. Only then would Alexander be hailed as the king of Greece and Persia. The rumors were that Darius, housed for the moment in Ecbatana over the mountains and deep in the heart of Persia, had already gathered with his senior officials and was working to raise yet another massive army. Having thought that Darius was cowed at Issus only to have him return in even greater force at Gaugamela, Alexander could not afford to make the same mistake again, and he set his sights on the ancient capitals of Persia, where he would encounter his toughest challenge yet as Persian Commander Ariobarzanes blocked the pass of the Persian Gates.

The Battle of the Persian Gate: The History of the Achaemenid Persian Empire’s Last Stand against Alexander the Great looks at one of antiquity’s most important battles.