The Achaemenid Empire c. 550–330 BC, also called the First Persian Empire, was an ancient Iranian empire based in Western Asia founded by Cyrus the Great. Ranging at its greatest extent from the Balkans in the west to the Indus Valley in the east, it was larger than any previous empire in history, spanning 5.5 (or 8) million square kilometers. Incorporating various peoples of different origins and faiths, it is notable for its successful model of a centralised, bureaucratic administration (through satraps under the King of Kings), for building infrastructure such as road systems and a postal system, the use of an official language across its territories, and the development of civil services and a large professional army. The empire's successes inspired similar systems in later empires
In the 6th and early part of the 5th century BC Persian horsemen were heavily influenced by the Scythians, were armed with bows and javelins, and fought as light cavalry.
In the second half of the 5th Century there was an increase in armoured cavalry, armed with spears (palta) for thrusting and throwing, and the virtual disappearance of cavalry archers. The change and development can be directly linked to the wars against the Greek armies in the west.
These horsemen usually carried two palta, made from cornel wood. One could be thrown, and the other used for thrusting. The cornel wood spears were also stronger than the Greek spears, and Xenophon describes an encounter between Greek and Persian cavalry in 396BC when the Persians fought successfully with their palta, while the Greek spears broke too easily.
Later developments were to occur, when the Persians faced Alexander the Great’s Macedonian cavalry. The long Macedonian thrusting spear (also made from Cornel wood) had a big advantage over the shorter Persian thrusting spear which is one of the reasons for the Macedonian success at the Graneikos.
Darius III in the preparations for Gaugamela, tried to equip more of his cavalry with longer spears, or Macedonian style lances and adopt much heavier armour, including partial armour for the horses.