Pilum

[18] Although the bending of its shank is commonly seen as an integral part of the weapon's design and as an intentional feature, little evidence suggests that.

The most commonly found artifacts suggest that the pilum was constructed to use the weight of the weapon to cause damage, most likely to be able to impale through armour and reach the enemy soldier's body.

Bishop wrote that the momentum of the pilum caused the shank to bend upon impact, and although unintended, that proved a useful characteristic of the weapon.

[19] However, a newer work by M. C. Bishop states that pila are "unlikely to bend under their own weight when thrown and striking a target or ground"; rather, human intervention such as improper removal of a pilum stuck in a target is responsible in some way, and Caesar's writings should be interpreted as the pilum bending when soldiers tried to remove them.

Pictorial evidence suggests that some versions of the weapon were weighted by a lead ball to increase penetrative power, but archaeological specimens of that design variant are not (so far) known.

[24] The effect of the pilum throw was to disrupt the enemy formation by attrition and by causing gaps to appear in any protective shield wall.

This resulted in the aforementioned gaps in the protective shield wall, which could then favour the short gladius in tight hand-to-hand mêlées.

Pila could also be used in hand-to-hand combat; one documented instance of this occurred at the Siege of Alesia, and another during Mark Antony's Parthian campaign.

[27] Some pila had small hand-guards, to protect the wielder if he intended to use it as a mêlée weapon, but apparently this was common.

[citation needed] The Roman writer Vegetius, in his work De re militari, wrote: As to the missile weapons of the infantry, they were javelins headed with a triangular sharp iron, eleven inches [279 mm] or a foot long, and were called piles.

The soldiers were particularly exercised in the use of this weapon, because when thrown with force and skill it often penetrated the shields of the foot and the cuirasses of the horse.

Vegetius wrote about a one-foot iron shaft because at his time, the pilum had disappeared and been replaced by similar shorter weapons such as the plumbata and spiculum.

Due in part to experimental archaeology, the design of the pilum is believed to have evolved to be armour-piercing; the pyramidal head would punch a small hole through an enemy shield, allowing the thin shank to pass through and penetrate far enough to wound the man behind it.