The Persian army was the military force of the ancient Persian Empire, known for its organization and diverse composition. It included soldiers from various regions, such as Medes, Lydians, and Egyptians, reflecting the empire's vast territory. The army was famous for its elite unit, the Immortals, who were always maintained at a strength of 10,000 soldiers. Under leaders like Cyrus the Great and Darius I, the Persian army expanded the empire significantly. They utilized advanced tactics and strategies, including cavalry and archers, which contributed to their success in battles against various adversaries, including the Greeks during the Greco-Persian Wars.