Battle of Arbela
The Battle of Arbela took place on October 1st, 331 B.C. and was the largest battle fought in Alexander the Great's campaign to conquer the Persian Empire. The Persians had assembled perhaps the largest army ever gathered, about 200,000 men taken from all over the Empire to meet Alexander's 47,000 men. Darius III the king of Persia made an overture of peace to Alexander where he would give him 30,000 gold talents, half of his kingdom, and his daughter's hand. Alexander refused.
Darius' best foot troops, his Greek mercenaries, had been almost destroyed at the Battle of Issus, forcing him to rely mainly on his cavalry, chariots, and elephants. He formed his massive force in two long, deep lines with cavalry on each flank. In the center were the remaining Greek mercenaries and his Royal Guard cavalry. Numerous chariots also lined the front of the entire army and a clump of elephants were in the center. Darius had expected a night attack, and kept his tired troops in position all night on September 30th. The Persians were also counting on their great length to come in around Alexander's forces and surround him. As the battle unfolded, the Macedonian army drifted to the right. The Persians tried to move accordingly, creating some gaps in their lines. Alexander charged. The Persians tried to envelop the around the Macedonian flanks but were repulsed by units Alexander had set up for exactly that purpose. Alexander attacked a wedge in the left center part of the Persian line and smashed completely through the line. Darius, in the path of the onslaught, fled. Panic spread through the Persian center and left and they gave way. Alexander had to contend with the Persian right which had pushed back his own troops through force of numbers, but the reserve had held and as Alexander smashed into the rear of the Persian attackers, it ended the threat and the battle. Alexander led his entire army in a full out pursuit of the fleeing Persians, scattering them hopelessly. Alexander suffered 500 men dead and 5,000 wounded. Persian losses are unknown but were at least 50,000 dead. The back of Persian resistance had been broken. After two devastating losses, they no longer had a viable army to stop Alexander.
Encyclopedia of Military History, Dupuy & Dupuy, 1979