The Phalanx
The phalanx was a key military formation in both Hellenic and Hellenistic armies. it was made up of hoplites in a square formation during the Hellenic period but later the troops in the formation became less armored for both economic reasons and for the ability to carry longer pikes or the spears used in the warfare. The phalanx was used mainly to hold back the enemy force so that they were diverted from the cavalry and therefore the cavalry could charge through the enemy lines and take the victory. The phalanx also allowed for a much smaller force to charge at a larger force with their phalanx formation and still hold them off.
The Cavalry
In the Hellenistic period the entire army was interdependent on itself and each part was required for a purpose. As explained above, the phalanx formed a diversion for the main part of the enemy's army, while light infantry and archers would reinforce and fill weak areas. The heavy cavalry, with Alexander the Great leading them or later another military leader, would then charge through a weak point in the offensive lines and route the enemy to claim victory. This worked until it became overused and opposing forces tried to use the same formations at the same time, then causing an end to cavalry in the Hellenistic age.