The Persian army consisted of infantry, cavalry and chariot troops, and later Greek mercenaries also began to be part of it. Even under Cyrus, cavalry regiments were formed, in which light military chariots were replaced with more durable ones, whose drawbars and wheels were equipped with sickles. The warriors who fought on them were dressed in strong armor. The light Persian cavalry was equipped with canvas carapace, scale armor, and armed with swords, bows, and shields. Heavy horsemen wore armor that covered the entire body of a warrior. In addition to swords, bows and shields, she was armed with long spears. The infantry was also divided into light and heavy. The light infantry was armed with spears, swords, bows, and shields, and clad in light armor; heavy infantry – with sabers, axes, axes and wore heavy armor.
The privileged part of the Persian army consisted of the so-called “immortal” detachments, formed only from Indians, Persians and Elamites. They had 2,000 selected horsemen, 2,000 spearmen on foot, and 10,000 foot soldiers. The personal bodyguard of the king, which consisted only of representatives of the Persian nobility, numbered a thousand soldiers.
The distinctive marks of the “immortals” were gold and silver balls set on the blunt ends of the spears. During the campaign in front of the troops carried a golden image of an eagle – the military sign of the Achaemenids.
The training of these warriors began as early as childhood, they were supposed to master weapons perfectly.
The bulk of the army was made up of the Persians, who began to serve at the age of twenty, as well as the Medes. The soldiers who were in the service received monthly payments for food and everything necessary. Those who retired received small plots of land and were exempted from paying taxes. In the event of war, the tsar collected a huge militia from all over the state: all the peoples inhabiting the huge Achaemenil empire were required to allocate a certain number of soldiers for this. In the conquered lands, the Persian kings stationed military garrisons; for example, in Egypt there was a permanent army of 10,000-12,000 people. According to Xenophon’s testimony (not later than 444 BC, – not earlier than 356 BC), the king annually inspected his army, which was located around the royal residence. In the satrapies, the reviews were carried out by specially appointed officials. For the good maintenance of the army, the tsar rewarded the satraps, for the bad – removed from office and severely punished.
Under Darius, a fleet appeared in Persia, and the Persians began to use Phoenician and later Egyptian ships for sea battles.