Imperial Army of Iran

With thousands of years of recorded history, and due to an unchanging geographic (and subsequently geopolitical) condition, Iran (previously known as Persia in the West until 1935) has had a long, varied, and checkered military culture and history, ranging from triumphant and unchallenged ancient military supremacy affording effective superpower status in its day, to a series of near catastrophic defeats (beginning with the destruction of Elam) at the hand of previously subdued and conquered peripheral nations (including Greece, Macedon and the Asiatic nomadic tribes at the Eastern boundary of the lands traditionally home to the Iranian people).

The Achaemenid Empire (559 BC–330 BC) was the first of the Persian Empires to rule over significant portions of Greater Iran. The empire possessed a “national army” of roughly 120.000-150.000 troops, plus several tens of thousands of troops from their allies.

The Persian army was divided into regiments of a thousand each, called hazarabam. Ten hazarabams formed a haivarabam, or division. The best known haivarabam were the Immortals, the King's personal guard division. The smallest unit was the ten man dathaba. Ten dathabas formed the hundred man sataba.

The royal army used a system of color uniforms to identify different units. A large variety of colors were used, some of the most common being yellow, purple, and blue. But this system was probably limited to native Persian troops and was not used for their numerous allies.

The usual tactic employed by the Persians in the early period of the empire, was to form a shield wall that archers could fire over. These troops (called sparabara, or shield-bearers) were equipped with a large rectangular wicker shield called a spara, and armed with a short spear, measuring around six feet long.

Though equipped and trained to conduct shock action (hand-to-hand combat with spears, axes and swords), this was a secondary capability and the Persians preferred to maintain their distance from the enemy in order to defeat him with superior missile-power. The bow was the preferred missile-weapon of the Persians. At maximum rate of fire a sparabara haivarabam of 10,000 men could launch approximately 100,000 arrows in a single minute and maintain this rate for a number of minutes. Typically the Persian cavalry would open the battle by harassing the enemy with hit and run attacks - shooting arrows and throwing small javelins - while the Persian sparabara formed up their battle-array. Then the Persian cavalry would move aside and attempt to harass the flanks of the enemy. Defending against the Persian cavalry required the enemy infantry to congregate in dense static formations, which were ideal targets for the Persian archers. Even heavily armoured infantry like the Greek hoplites would suffer heavy casualties in such conditions. Enemy infantry formations that scattered to reduce casualties from the dense volleys of Persian arrows, were exposed to a close-in shock assault by the Persian cavalry. Torn by the dilemma between exposure to a gradual attrition by the arrows or to being overwhelmed by a cavalry charge on their flanks, most armies faced by the Persians succumbed.

...
Wikipedia