The pilum had an iron shank with a pyramidal head, The shank was secured to a wooden shaft, either by means of a socket or a tang. The pilum was about 2 meters (6.6 feet) long and weighed between 2 and 5 kilograms (4.4 to 11 lbs).
Though it could be used as a melee weapon, the pilum was primarily a throwing spear. The pilum had a maximum distance of around 100 feet (30 meters) though the effective range was 50 to 65 feet (15 to 20 meters). The pilum was designed so that the shank bent or broke off from the wooden shaft on impact to prevent the opponent from throwing it back at the Romans or to get stuck into enemy shields. The weight of the pilum would make the enemy shield too combersome to be used.