The pilum (plural: pila) was a javelin commonly used by the Roman army in ancient times. It was generally about two meters long, consisting of an iron shank about seven millimeters in diameter and sixty centimeters long with a pyramidal head. The shank was joined to the wooden shaft by either a socket or a flat tang.
The Heroes of Olympus[]
The Son of Neptune[]
When Percy Jackson just joined the Twelfth Legion, during the war games, most of the legionnaires carried pila and other weapons like the gladius and daggers. As described in the book, pila are "harpoon-like" weapons. After the games are won, Gwendolyn is found to have been murdered with a pilum which is implied to have been done by Octavian who is noticeably missing his. However, Gwen is able to resurrect herself because the Doors of Death are open and Thanatos is chained up. When the pilum is removed from Gwen's body after her resurrection, the wound immediately heals up.
After Percy and his companions Frank Zhang and Hazel Levesque returned from their quest in Alaska, the Romans were fighting with the army of Gaea, and some used pila.