It was a developing technology before him. Philip, when he was young, was a hostage of Thebes. Thebes at this time was the strongest City-State in Greece after they defeated the Spartans. Epaminondas was the leader of Thebes and he started to implement a longer spear in his army. This spear was about 12 feet long and Philip later took this idea and adapted it into the 18 foot sarissa.