What battle tactics made the Persian Empire's army so effective?

Answer 1

The most effective tactic was bribery - to gain submission by bribing the opposition leaders to submit, or some to desert on the battlefield leaving the rest in disarray.

If it became necessary to fight, the object was to hold ground with infantry and use cavalry against the flanks and rear of the opposition.

A further means was to use allies or subject people to provide specialist support. The Persians were not seafaring, and their navy was mainly made up of Phoenicians, Egyptians and Greeks.

The use of combined naval and army forces enabled them to pose an amphibious threat against the home cities of opponents, who kept their main forces at home as protection, which gave the Persian army reduced opposition.

Answer 2

The Persian Empire's effectiveness was first seen when fighting against a phalanx battle formation. With overhead fire of arrows, even the second line of ranks were able to shoot arrows at a high level and harm an enemy phalanx's beyond its front ranks. The Persians also grouped their light infantry in a shallow line, and the troops were equipped with large wicker shields for protection against the enemy's arrows. This unit was highly mobile and caused an enemy to be confused when the Persian cavalry, armed with short spears, bows or javelins assaulted the enemy's flanks. These two systems relied on mobility. Unlike the Greeks, the Persians made little use of heavy infantry.