The spear in Caesar is a hybrid between a more traditional Roman javelin (pilum) and a leaf-bladed spear. This choice was made to aid in the readability of the spear in gameplay. The pilum-shank in historical pieces is very thin and this makes the end of the pilum hard to see. A large flat leaf-blade spear shape made more sense and enables you to easily see where you are stabbing. Pila were used most commonly by infantry and were thrown at an advancing infantry/cavalry force to thin them out before advancing with gladius. Soldiers would often have multiple pila for multiple volleys before engagement. Pila could also be used in melee, but his is rarer due to the frail nature of their shank. Thus the thicker leaf-bladed spear hybrid is a superior weapon for the one man army Caesar.
The Spear like all planned weapons in Ceasar has two alternative attacks. The first is a jab or stabbing attack. It Is slower than the primary attack on the gladius but has a longer range. This attack only targets one enemy at a time but will knock enemies back away from you as well as dealing damage. The second attack is a throw, at any time in combat you can opt to throw your spear. The spear throw is devastating and can be used to kill a large number of enemies in aimed correctly. An airborne spear hurled by Caesar will travel indefinitely until it contacts a wall. This makes spear throwing an excellent way to make shish kebabs out of any number of foes. Spears are accumulated as ammo and cannot be picked up again once thrown, so use your spears wisely. Check out the spear model on sketchfab: below: