Darius III was a ruler of the Persian Empire most well-known for losing that empire to Alexander the Great.

Darius was born in 380 B.C. as Artashata and was known also as Codomannus. His mother was Sisygambis, whose father was King Artaxerxes II. Darius had early experience in governing and fighting when he served in the army, advancing to the rank of general, and as a satrap, ruling in Armenia. He also had experience as a royal courier.

Darius came to the throne through the machinations of a man named Bagoas, who in the 330s was vizier, one of the empire's highest-ranking officials. Contemporary sources say that Bagoas poisoned then-King Artaxerxes III, in 338 B.C., and then administered the same treatment to his son, Artaxerxes IV, two years later. Bagoas wanted to the power behind the throne and thought that Darius would allow him to do it; when Darius proved none too willing, Bagoas tried to poison him as well. The king forced his vizier to drink his own poison, ending the threat. Thus, in 336 B.C., at age 43, Darius was firmly on the throne. He had taken the name Darius when he took the throne, to emulate two previous emperors, including Darius the Great.

At the same time, King Philip II of Macedon was organizing an invasion of Asia Minor, in retaliation for actions that the invading Persian armies of Darius the Great and Xerxes the Gerat had taken 150 years before. Philip was killed before he could start the invasion, and his young son Alexander took the reins of both the kingdom and the invasion force.

Darius III, as it turned out, had a higher opinion of his own abilities and those of his satraps and military commanders than was warranted. Despite the presence of a massive army of well trained men and a very large number of ships full of well trained fighters, Darius found himself again and again on the losing end of struggles against a much smaller Macedonian force.

The first hint of trouble for Darius occurred not long after the Macedonian invaders crossed the Hellespont. In one of the few battles in which Macedonians outnumbered Persians, Alexander and his men won a victory at Granicus. Darius had delegated the fighting to his generals and so was not on the battlefield.

Alexander next marched his men along the Mediterranean coast, seizing more coastal cities, this time on the Phoenician coast. One of his main targets was Sidon, the port city that served as the shipyards for the Persian invasions of Egypt and Greece. In 351 B.C., the people of Sidon locked their gates and set fire to the city rather than submit to the Persian leader Artaxerxes. This, of course, made it easer for Alexander to conquer.

While the Macedonian king was forcing his way into Sidon and Byblos, Darius was rallying an army 100,000 strong and marching down the Phoenician coast after Alexander. Darius's goals were twofold: intercept Alexander's supply lines and trap the invaders far from home, where they were less likely to put up a fight. Darius got all of what he wanted, except for the last part, the intangible part, which proved to be his undoing in the end. For not the last time, Darius underestimated Alexander.

The Macedonians turned quickly around and marched north. Alexander, kicking himself for assuming that Darius wouldn't come after him, forced his men to march double quick, overnight, for many miles. The two armies met in the Battle of Issus.

It should have been a Persian victory. Darius had more men, who were rested. He had picked the place where he wanted to fight. He was in a defensive position, which Alexander had to attack. In fact, many historians argue, Darius didn't really have to win at all; he just had to avoid losing. If the battle resulted in a standoff, then Alexander would be forced to retreat—toward more Persian forces, coming up from the southeast. But Darius didn't play to tie; he played to win. And this decision cost him dearly.

First of all, Darius deployed his men on a narrow coastal plain, meaning that they would fight in rows, not in a mass formation. Clearly, he did choose the terrain with the idea of using all of his men at once in a mass, hard charge. Secondly, Alexander noticed that Darius had deployed archers near a group of inexperienced young Persian soldiers on the left flank of the main army, where Darius himself stood, in the center. Alexander reasoned that the archers were there because the soldiers couldn't hold the field by themselves. So while the rest of the battlefield raged with hand-to-hand blows, Alexander led his cavalry in a fierce assault on those archers and the experienced infantry they were protecting. Like a carpet, the young Persians folded up and disappeared, with the Macedonian cavalry in hot pursuit. So devastating was the cavalry charge that the entire Persian left flank disappeared, leaving the cavalry with a straight shot at Darius, who quickly led his men in retreat. The emperor, who had counted on a successful defense turning into victory, now found himself in crushing defeat, his armies in full flight, his confidence shattered, the territory he owned rapidly shrinking.

All of this happened so quickly that Alexander and his men acquired many great spoils from this victory, including the entire royal family—Queen Stateira, Queen Mother Sisygambis, Princess Stateira, and Darius's other children. They remained prisoners of Alexander and his men for a very long time.

With all of the other major settlements in the fold, Alexander now had one major obstacle left to his goal of ruling the entire eastern Mediterranean: Tyre, which he did so with devastating fury, building a causeway out to the island and then sacking the city.

While Alexander was conquering Tyre and Egypt (which he took without so much as a fight in 332 B.C.), Darius was getting ready for the next confrontation. Darius desperately wanted to avoid the mistakes that led to his defeat at Issus. He was still the emperor of the Persian Empire, and he still commanded an army of many thousands. (Some historians, notably Arrian, claim that the Persian army numbered 1 million at this battle.) He could still also choose the field of battle. At Gaugamela, he chose a wide open plain, in which he could deploy his entire army to its best effect.

By this time, Alexander was flush with victory again, having rolled up much of the western part of what used to be the empire. He still hadn't lost a battle and was considered a military genius who would take any advantage in order to win the day. He had still inferior numbers, but that hadn't stopped him from winning before. One of Alexander's commanders, a man named Parmenion, advised Alexander to attack at night and gain the element of surprise. Alexander decided against it, but Darius feared that sort of attack all too well and kept his men standing on the battlefield all night. Fearing the worst, Darius created the worst. Alexander and his men, on the other hand, had a good night's sleep.

The battle unfolded in much the same way as the Battle of Issus, with the Persians taking early advantage and then Alexander's cavalry delivering a knockout blow near the end. The deciding factor again was Alexander's ability to see what was happening during the fighting and shift resources were they were needed most or could take full advantage. In an era of communication by messenger and long before aerial reconnaissance, this ability of Alexander's was a prime factor in his being able to win when winning seemed out of the question. Alexander's victory at Gaugamela, however, viewed from Darius's point of view, must have been all the more puzzling, especially since the emperor was sporting some surprise new weapons this time around: some war elephants imported from India and 200 fully armed war chariots. The Macedonian army made quick work of it all, though, and drove their point home. Darius, again, was sent packing, far to the east.

Before the battle, Darius had offered the hand of his daughter in marriage to Alexander, as well as a large ransom in order to get his family back. Alexander rejected both requests. After the disaster at Gaugamela, Darius was abandoned by his troops and fled for safety to Erbil, in what is now Iraq. He moed then to Ectabana and then Bactria, in an effort to more effectively confront the Macedonian threat. The satrap of that province, Bessus, is the one who dispatched Darius. He and two other co-conspirators seized Darius, threw him in an oxcart, and then stabbed him, leaving him to die, giving him none of the ceremony that an emperor should have had. In fact, Bessus took the throne for himself and declared himself King Artaxerxes V.

Alexander, in pursuit, found Darius dead. Alexander took the king's ring from Darius's finger and ordered his body sent to Persepolis, to be buried in a royal tomb. The conqueror then fulfilled the conquered king's wish and married his daughter, Stateira.