Wikipedia
The Sparabara, meaning "shield bearers" in Persian, were the heavy front line infantry of the Achaemenid Persian Empire. They were usually the first to engage in hand-to-hand combat with the enemy. Although not much is known about them today, it is believed that they were the backbone of the Persian army who formed a shield wall and used their two-metre-long spears to protect more vulnerable troops such as archers from the enemy.
The Sparabara were taken from the full members of Persian society, they were trained from childhood to be soldiers and when not called out to fight on campaigns in distant lands they practised hunting on the vast plains of Persia. However, when all was quiet and the Pax Persica held true, the Sparabara returned to normal life farming the land and grazing their herds. Because of this they lacked true professional quality on the battlefield, yet they were well trained and courageous to the point of holding the line in most situations long enough for a counterattack.
They were armoured with quilted linen and carried large rectangular wicker shields as a form of light manoeuvrable defense. This, however, left them at a severe disadvantage against heavily armoured opponents such as the hoplite, and his two-metre-long spear was not able to give the Sparabara ample range to plausibly engage a trained phalanx. The wicker shields were able to effectively stop arrows but not strong enough to protect the soldier from spears. However, the Sparabara could deal with most other infantry, including trained units from the East.