The Parthian Empire, which succeeded the Achaemenids, was known for its expertise in archery on horseback. This form of warfare, known as horse archery or mounted archery, played a significant role in the military success of the Parthians.

The Parthians were a nomadic people who originated from the Eurasian Steppe, where horse archery was a traditional and essential skill for survival and warfare. They brought this expertise with them when they established their empire in the region that is present-day Iran and Iraq.

Here is an explanation of why archery on horseback became a defining feature of Parthian warfare:

1. Strategic Mobility: Horse archery allowed the Parthian warriors to swiftly move across vast distances, enabling them to conduct hit-and-run tactics and surprise attacks. This mobility provided a significant advantage over their enemies, who were often slower and less maneuverable.

2. Superior Archery Skills: The Parthians were renowned for their exceptional archery skills. They were able to accurately shoot arrows while riding at high speeds, making them deadly opponents. This skill was honed through years of practice and training from early childhood.

3. Tactical Flexibility: The Parthians employed a tactic known as the "Parthian Shot," which involved feigning retreat and then turning around to shoot arrows at their pursuers. This maneuver caught their enemies off guard and often resulted in devastating losses. The ability to shoot arrows in multiple directions while on horseback gave them a distinct advantage in battle.

4. Psychological Warfare: The Parthians' expertise in horse archery also had a psychological impact on their enemies. The sight of a large number of mounted archers riding towards them, shooting arrows with great precision, created fear and panic among their opponents. This psychological advantage often demoralized the enemy forces and weakened their resolve to fight.

In conclusion, archery on horseback was the form of warfare in which the Parthian Empire excelled. Their mastery of this skill, along with strategic mobility, superior archery skills, tactical flexibility, and psychological warfare, enabled them to establish a formidable empire and maintain their dominance in the region for several centuries.