Alexander the Great.

This is coolbert:

The first commander to make use of what it now called combined arms was Alexander the Great.

Macedonian King and general par excellence who conquered much of the known world with an army that maybe numbered only at maximum 30,000 men.

This was a professional force carefully put together and sustained by the father of Alexander, Phillip of Macedon. Using the infantry, cavalry, and artillery of the day [slingers, javelin throwers, archers, catapults, etc.] fighting in unison as part of an overall plan in battle.

The concept of combined arms is often described as being analogous to the child's game of paper, stone, and scissors. You know! Paper covers the stone, scissors cuts the paper, and stone breaks the scissors. Each item defeats one of the other two and in turn is defeated by another. Complementary protection and enhancement.

These type of units and weapons had been used by the armies of the time all over the world for some time. Were known and used to varying degrees, and had been employed by previous militaries, but not used in the same fashion as was employed by Alexander.

Fighting a running battle against his foe, Alexander used each combat arm as part of the whole, supporting and protecting and enhancing the inherent strength of each.

Infantry [heavily armored foot troops] moved forward on the battlefield, supported by artillery firing a barrage of arrows, javelins, stones flung by peltists [sling throwers], and large boulder sized objects thrown by catapults [Alexander's catapults were mobile. Could be broken down and transported by horse and assembled at the battlefield just prior to battle] on the enemy. 

Cavalry would safeguard the flanks of the infantry and also the rear of the Macedonian force, acting as a guard and protector for the artillery. Cavalry would also be called upon to attack the enemy rear or to exploit gaps in the enemy defenses created by infantry assault, that assault being supported by the artillery arm.

A similar combined arms concept exists on the modern battlefield. Infantry moves forward and is stopped by the machinegun. The machine gun is countered by armor, which in turn is countered by anti-tank guided missiles [ATGM]. The ATGM in turn is countered by artillery, the artillery being attacked by enemy aircraft, which are defended against by air defense.

coolbert.