The stirrup wasn't invented yet. Putting a limit on how much armour a rider can wear, and how 'hard' he can be engaged in battle. When we read about Alexander t

The stirrup wasn't invented yet. Putting a limit on how much armour a rider can wear, and how 'hard' he can be engaged in battle. When we read about Alexander the Great leading his cavalry in a charge we shouldn't think of medieval knights crashing into the line. But rather north American natives getting close and pulling back, while prodding and poking with their spears. The chariot doesn't have that problem, so there is definitely an use for both chariots and cavalry.