Before the Iron Age, the role of cavalry on the battlefield was largely performed by light chariots. The power of mobility given by mounted units was recognized early on, but was offset by the difficulty of raising large forces and by the inability of horses (then mostly small) to carry heavy armor.
The chariot was first adopted by nomadic or semi-nomadic peoples on the boundaries of civilization in conflicts with civilized peoples. The chariot was quickly adopted by settled peoples both as a military technology and an object of ceremonial status. Pharaoh rides a chariot into battle in the Egyptian New Kingdom, just as the Sun rides a chariot over the sky in Egyptian mythology.
Chariots were quickly superseded by horses when selective breeding resulted in horses able to carry the weight of a fighting man.