Battle of Gaugamela or Arbela 331 BC : Alexander the Great defeats the Persians

The Battle of Gaugamela, also called the Battle of Arbela, was the decisive battle of Alexander the Great's invasion of the Persian Achaemenid Empire. In 331 BC Alexander's army of the Hellenic League met the Persian army of Darius III near Gaugamela, close to the modern city of Erbil (Iraqi Kurdistan) . Even though heavily outnumbered, Alexander emerged victorious due to his superior tactics and army. It was a decisive victory for the Hellenic League and led to the fall of the Achaemenid Empire. After settling affairs in Egypt, Alexander returned to Tyre during the spring of 331 BC. He reached Thapsacus in July or August of 331 BC. Arrian relates that Darius had ordered Mazaeus to guard the crossing of the Euphrates near Thapsacus with a force of 3,000 cavalry. He fled when Alexander's army approached to cross the river. After crossing the Euphrates Alexander followed a northern route instead of a direct southeastern route to Babylon. While doing so, he had the Euphrates and the mountains of Armenia on his left. The northern route made it easier to forage for supplies and did not feature the extreme heat of the direct route. When some Persian scouts were captured, they reported to the Macedonians that Darius had encamped past the Tigris river and wanted to prevent Alexander from crossing. Alexander found the Tigris undefended and succeeded in crossing it with great difficulty. After the Macedonian army had crossed the Tigris a lunar eclipse occurred. Following the calculations, the date must have been October 1 in 331 BC. Alexander then marched southwards along the eastern bank of the Tigris. On the fourth day after the crossing of the Tigris his scouts reported that Persian cavalry had been spotted, numbering no more than thousand men. When Alexander attacked them with his cavalry force ahead of the rest of his army, the Persian cavalry fled. Most of them escaped, but a few were slain or taken prisoner. The prisoners told the Macedonians that Darius was not far away, with his encampment near Gaugamela. According to Arrian, Darius's force numbered 40,000 cavalry and 1,000,000 infantry, Diodorus Siculus put it at 200,000 cavalry and 800,000 infantry, Plutarch put it at 1,000,000 troops(without a breakdown in composition), while according to Curtius Rufus it consisted of 45,000 cavalry and 200,000 infantry. Furthermore, according to Arrian, Diodorus, and Curtius, Darius had 200 chariots while Arrian mentions 15 war elephants. Included in Darius's infantry were about 2,000 Greek mercenary hoplites. While Darius had a significant advantage in numbers, most of his troops were of a lower quality than Alexander's. Alexander's pezhetairoi were armed with a six-metre pike, the sarissa. The main Persian infantry was poorly trained and equipped in comparison to Alexander's pezhetairoi and hoplites. The only respectable infantry Darius had were his 2,000 Greek hoplites and his personal bodyguard, the 10,000 Persian Immortals. The Greek mercenaries fought in a phalanx, armed with a heavy shield but with spears no longer than three metres, while the spears of the Immortals were 2 metres long. Among the other Persian troops, the most heavily armed were the Armenians who were armed the Greek way, and probably fought as a phalanx. The rest of Darius's contingents were much more lightly armed; the main weapon of the Achaemenid army historically was the bow and arrow, and javelin. Alexander began by ordering his infantry to march in phalanx formation towards the center of the enemy line. The Macedonian advanced with the wings echeloned back at 45 degrees to lure the Persian cavalry to attack. While the phalanxes battled the Persian infantry, Darius sent a large part of his cavalry and some of his regular infantry to attack Parmenion's forces on the left. During the battle Alexander used an unusual strategy which has been duplicated only a few times. While the infantry battled the Persian troops in the center, Alexander began to ride all the way to the edge of the right flank, accompanied by his Companion Cavalry. His plan was to draw as much of the Persian cavalry as possible to the flanks, to create a gap within the enemy line where a decisive blow could then be struck at Darius in the center. This required almost perfect timing and maneuvering, and Alexander himself to act first. Alexander would force Darius to attack (as they would soon move off the prepared ground) though Darius did not want to be the first to attack after seeing what happened at Issus against a similar formation. In the end Darius' hand was forced, and he attacked. As the Persians advanced farther and farther to the Greek flanks in their attack, Alexander slowly filtered in his rearguard. Alexander disengaged his Companions, and prepared for the decisive attack. Behind them were the guards brigade along with any phalanx battalions he could withdraw from the battle. He formed his units into a giant wedge, with him leading the charge. The Persian infantry at the center were still fighting the phalanxes, hindering any attempts to counter Alexander's charge. This large wedge then smashed into the weakened Persian center, taking out Darius's royal guard and the Greek mercenaries. Darius was in danger of being cut off, and the widely held modern view is that he now broke and ran, with the rest of his army following him. Alexander could have pursued Darius at this point. However, he received desperate messages from Parmenion (an event which would later be used by Callisthenes and others to discredit Parmenion) on the left. Parmenion's wing was apparently encircled by the cavalry of the Persian right wing, and being attacked from all sides were in a state of confusion. Alexander was faced with the choice of pursuing Darius and having the chance of killing him, ending the war in one stroke, but at the risk of losing his army, or going back to the left flank to aid Parmenion and preserve his forces, thus letting Darius escape to the surrounding mountains. He decided to help Parmenion, and followed Darius later. While holding on the left, a gap had opened up between the left and center of the Macedonian phalanx, due to Simmias' brigade of pezhetairoi being unable to follow Alexander in his decisive attack, as they were being hard pressed. The Persian and Indian cavalry in the center with Darius broke through. Instead of taking the phalanx or Parmenion in the rear, they continued towards the camp to loot. They also tried to rescue the Queen Mother, Sisygambis, but she refused to go with them. These raiders were in turn attacked and dispersed by the rear reserve phalanx as they were looting. What happened next was described by Arrian as the fiercest engagement of the battle, as Alexander and his companions encountered the cavalry of the Persian right, composed of Indians, Parthians and "the bravest and most numerous division of the Persians", desperately trying to get through to escape. Sixty Companions were slain in the engagement, and Hephaestion, Coenus and Menidas were all injured. Alexander prevailed, however, and Mazaeus also began to pull his forces back as Bessus had. However, unlike on the left with Bessus, the Persians soon fell into disorder as the Thessalians and other cavalry units charged forward at their fleeing enemy.  After the battle, Parmenion rounded up the Persian baggage train while Alexander and his bodyguard pursued Darius. As at Issus, substantial loot was gained, with 4,000 talents captured, the King's personal chariot and bow, and the war elephants. It was a disastrous defeat for the Persians and one of Alexander's finest victories. Darius managed to escape with a small corps of his forces remaining intact. The Bactrian cavalry and Bessus caught up with him, as did some of the survivors of the Royal Guard and 2,000 Greek mercenaries. At this point, the Persian Empire was divided into two halves–East and West. On his escape, Darius gave a speech to what remained of his army. He planned to head further east and raise another army to face Alexander, assuming that the Greeks would head towards Babylon. At the same time, he dispatched letters to his eastern satraps asking them to remain loyal. The satraps, however, had other intentions. Bessus murdered Darius before fleeing eastwards. When Alexander discovered Darius murdered, he was saddened to see an enemy he respected killed in such a fashion, and gave Darius a full burial ceremony at Persepolis, the former ceremonial capital of the Persian Empire, before angrily pursuing Bessus, capturing and executing him the following year. The majority of the remaining satraps gave their loyalty to Alexander and were allowed to keep their positions. The Achaemenid Persian Empire is traditionally considered to have ended with the death of Darius.
Πηγή: https://en.m.wikipedia.org/wiki/Battle_of_Gaugamela