From the website Warfare in Hellas
http://monolith.dnsalias.org/~marsares/w...egrat.html
The integrated army
The evolution of battlefield tactics peaked with the integrated army of multiple arms. Each arm had a battlefield role and mission. The army that best employed its various parts, using its rocks to break the enemies scissors, had the best chance of victory. An army that was not integrated, like the Greek phalanx armies, or an army only partially integrated, was at great risk because it might be at a significant disadvantage on offense, defense, or both.
Assyrians
Integrated armies were first deployed in Mesopotamia during the second millennium. The Assyrians, especially, learned by trial and error to use infantry, skirmishers, chariots, and cavalry in battle simultaneously because they had to face a wide spectrum of enemies. They fought advanced chariot armies to their south and northwest (the Babylonians and Hittites) and barbarians to their west, east, and north. They had enemies in every direction and learned new techniques from fighting each. The best weapons, formations, and tactics from each were adopted or foreign troops were hired as mercenaries to supplement the army.
Alexander the Great
The greatest integrated army of antiquity was probably that of Alexander the Great. This army combined heavy hoplite infantry, heavy cavalry (the Companions), light cavalry, skirmishers, and light troops from several different cultures into an integrated whole. Under the brilliant tactical and strategic leadership of Alexander, the army conquered Greece, Anatolia, the Levant, Mesopotamia, Egypt, and the Indus Valley in the incredibly short period of 10 years (336 BC to 326 BC). Alexander consistently used the parts of his army to perfection, employing the various units where they had the best chance of success. He was successful in all the battles he fought, even though he was usually outnumbered significantly.