Fan-made Card depicting the Chariot Archer Unit from Civ5
Game Info
First mounted unit of the game. Has a ranged attack. Requires 
Horses Horses.
- Common abilities:
- May Not Melee Attack
- No Defensive Terrain Bonuses
- Rough Terrain Penalty (Entering rough terrain consumes all movement.)
Strategy
Chariot Archers are fast ranged units, deadly on open terrain, and the first unit to require a strategic resource - Horses. They are more powerful than the Archer and can move twice the distance on open terrain (4 MPs), allowing them to reach elements of the enemy army other units can't. However, Chariot Archers suffer a horrible movement penalty when entering forest, jungle, or hill tiles unless roads have been constructed in them. (They suffer the normal movement penalty when moving through marsh tiles rather than losing their resting MPs, since these are not considered to be rough terrain.) Moreover, they're too bulky to use natural terrain defense, and unlike other mounted units, cannot move after attacking!
Use the Chariot Archers to explore the world and deal with Barbarians. Against other civilizations, they're excellent at getting into privileged positions and raining fire on the enemy from afar, but defend them with melee units against the enemy's melee fighters - they are weak in close combat! However, despite appearances, and information given in the Civilopedia, they are not considered to be a mounted unit, and so are not abnormally vulnerable to Spearmen.
There is one more important detail to remember: Chariot Archers and all of their unique alternatives - Hunnic Horse Archers, Egyptian War Chariots, and Indian War Elephants - are ranged units, and receive promotions as such. However, come the Medieval Era, they will all upgrade to Knights, which are mounted units with melee attacks! This means that all attack-oriented promotions the unit received will suddenly become useless, since it now attacks in melee, not from a distance! To circumvent this annoying fault, try to choose non-attacking promotions, such as Cover, which will remain useful after the unit changes its attack mode.
Civilopedia entry
Before the invention of the stirrup, it was virtually impossible to fight from horseback. There was no way to brace oneself, and the slightest push could unhorse the warrior, with disastrous results. Horses first appeared on the battlefield pulling chariots. A chariot team usually consisted of one or two horses, a driver, and an archer. The chariots' mobility made them especially dangerous to infantry: they could rush within range, fire off a volley, then escape before the foot-bound soldiers could close with them. The greatest weakness of a chariot archer team was its inability to deal with difficult terrain. On open plains they were the kings of the ancient battlefield; in hills or woods they were at a significant disadvantage.