How was the Persian army organized?

In ancient times, the Persian army was one of the strongest in the ancient east. The Persian army was divided into the following types: infantry, cavalry and navy. Infantry units were divided into lightly armed and heavily armed. Also, the main striking force of the Persian troops was the personal guard of the kings – immortals. The cavalry was also divided into light and heavy, in addition, there were also chariots, and sometimes the Persian kings hired war elephants in their army.