How did Alexander the Great beat Persia in gaugamela

Before the battle, Macedonian scouts had reported an overwhelming numerical superiority of the Persian forces and the works ordered by king Darius to flatten out the site he chose for the battlefield so that his chariots had no trouble traversing it. Parmenion, Alexander's most veteran general, advised to launch an attack at night in order to make up for the numerical disadvantage, Alexander rejected the plan since he fell it would away the full glory out of his victory. Instead, he came up with an unusual strategy: he had his lines of sarissa lancers form obliquely with respect to the Persian lines, so the right flank would be closer to the enemy and the left one further away. In addition, he instructed his troops to allow the chariots to pass through their lines by stepping aside of their way and had light infantry troops armed with slingshots take out the chariot drivers and lancers.

As Alexander had expected, Darius ordered his chariots to attack and were put out of combat quickly. As the two armies came closer to each other, Alexander and his cavalry corps of Companions dashed at full gallop from the right flank with one sole objective: find Darius to capture him or kill him so that the Persian army was thrown into disarray once their commander was gone. As Alexander himself came a few yards close to Darius, Darius panicked and fled from the battlefield right away, which demoralized and threw the Persians into disarray. Alexander was about to go after Darius when he learned that general Parmenion's units were in badly need of support, so Alexander decided to come and rescue his troops. However, the word of Darius's fleeing the battlefield quickly spread throughout the Persian army which lost coherence and was routed afterwards.