"Maniples" were units of 120 men each drawn from a single infantry class. The maniples were small enough to permit tactical movement of individual infantry units on the battlefield within the framework of the greater army. The maniples were typically deployed into three discrete lines (Latin: "triplex acies") based on the three heavy infantry types of "hastati", "principes" and "triarii". The first type, the "hastati", typically formed the first rank in battle formation. They typically wore a brass chest plate (though some could afford mail), a helmet called a galea, and occasionally, greaves (shin guards). They carried an iron bossed wooden shield, 120 cm (4 ft) tall and rectangular in shape with a curved front to partially protect the sides. Traditionally they were armed with a sword known as a "gladius" and two throwing spears known as "pila": one the heavy "pilum" of popular imagination and one a slender javelin. However the exact introduction of the "gladius" and the replacement of the spear with the sword as the primary weapon of the Roman legions is uncertain, and it's possible that the early manipular legions still fought with the "hastati" and "principes" wielding the "hasta" or spear.