The Parthians
Formed from the Achaemenid Persians and Scythian inspired nomads, the Parthian military bore a resemblance to the military societies of the Middle Ages. Dominated by heavy cavalry, who were accompanied by lightly armored horse archers, it only used infantry in times of protracted war. The Parthians adopted these tactics after their defeat at the hands of Alexander the great. They realized that only heavily armored cavalry stood a chance against the hoplite infantry. So they developed a system where the cavalry broke into the ranks of enemy infantry, causing them to scatter so they could be picked off by the lightly armored bowmen.
The Parthian archers were particularly renown for one particular skill: the Parthian shot. When in retreat- real or by design, the Parthian mounted archers s would send their horses into a full gallop. They would fully turn their bodies around in the saddle, so they faced the enemy and then fired upon them. This was achieved without stirrups for support, using just the knees pressed against the saddle to support the rider.
However, horses were themselves vulnerable in battle. So the Parthians took measures to protect them by providing the horses themselves with armor. Cassius Dio describes how the Parthians covered their horses with light metal armor that covered their “head, neck, chest and sides.” This light, flexible mail, made from overlapping leafs of metal was light and flexible enough not to impede the horse’s movement but still made it harder to bring the rider by injuring the horse.
Using these means, the Parthians were able to claim Iran back from the Seleucid Empire. Then came their encounters with the Romans. At the battle of Carrhea in 53BC, Parthian forces consisting of 1000 heavy cavalrymen and over 9000 horseback archers defeated the Roman general Crassus. Using their cavalry to scatter the Roman forces, the Parthians were able to defeat the Romans- despite the fact they were greatly outnumbered. The occasion marked the beginning of three centuries of conflict between Rome and the Parthians- until the Parthians themselves succumbed to another empire.