What kind of armor did the ancient Persians have?

Answer 1

Their infantry usually had wicker shields, quilted vests and a variety of helmets. This left them at a serious disadvantage to Greek infantry with metal body armour and the Macedonian phalanx which was essentially a spear and shield wall.

They tried to even this by drafting Greeks located within their empire during the Persian War 499-450 BCE, but didn't have the numbers to match the Greek city coalitions; then against Macedonia they hired Greek armoured mercenaries, but Alexander slaughtered the prisoners after the first battle in 334 BCE as a warning to Greeks not to go into Persian service. A final effort at Gaugamela in 331 BCE to use new specially-trained armoured soldiers opaquely called Cardakes also failed to deliver experienced armoured soldiers capable of standing up to the seasoned Macedonians.

Answer 2

The Persian Empire under the Achaemenids (its most famous period) used an army of mercenaries recruited from all corners of the huge empire. Each company of such an army would specialise in the fighting technique characteristic of its region: Scythian archers and peltasts, Libyan heavy charioteers, and so on.

The core of the Achaemenid army was probably the Immortals: heavy infantry equipped with light mail cuirasses and wicker shields which were light to manoeuvre and effective against arrows from composite bows.

A major reason for the Achaemenid defeats when they tried to annexe Greece under Darius and Xerxes was that the Immortals - though deadly against armies with no heavy infantry of their own - proved flimsy against Greek hoplites, who had developed the heavy infantry theory much further by furnishing their troops with wooden shields reinforced with bronze and organising them in the near-impenetrable phalanx infantry formation.