Ballistics improves the accuracy of all ranged units by enabling them to hit moving targets more precisely. It can only be researched from the Government Center and is needed to develop the technology that upgrades Guard Towers to Ballista Towers. However, the only unit that is precise without researching this technology is the Mirror Tower.
It is available to all civilizations except the Persians and Shang.
The "improved accuracy" works by making an archer, siege unit, warship or Tower fire at where a unit is going to be (assuming they continue moving in the same way) rather than where they are. So if an archer tries to fire at a cavalry unit moving in a straight line past him where each shot would ordinarily miss, each shot would hit instead. This is particularly useful against the enemy AI. With Ballistics, the unit being targeted may still be able to dodge the projectiles, if the player controlling it would manuever and change the unit's movement pattern instead. This would require great micromanagement skills, though.
The use of missile weapons for war presented challenges that hunting with the bow did not. Hunters stalked game and shot ideally at a stationary target. War targets were often armored, partially shielded, or moving. Effective use of the bow and other missile weapons required tactics and training. Bowmen of low skill were taught to fire in barrages at an area rather than at specific targets. Better- trained archers learned to shoot for specific parts of the target, including the horses of chariots or cavalry. Ballistics, the study of projectile flight, was derived from the name of an ancient missile weapon, the Ballista.