The Spearman appears in Stone Age to replace the Clubmen as an bulk of the force, being capable of defeating the Clubman, thanks to its pierce attack and shock armour. Slingers will make quick work of this unit, however.
In the Copper age, the Spearman continues to work as an main soldier, but the improved stats of the Maceman can prove to be a trouble to it. Simple Bowmen are also very dangerous to it. With the Horseman, the first Cavalry unit appears. The Spearman is the main counter for it.
The Spearman and its upgrades (Phalanx,Pikeman,Halberdier) exists from the Stone Age until the Industrial Age, after which the unit becomes obsolete together with the last Cavalry units. Due to its comparatively long lifespan of 8 epochs, Civilization bonuses are well spent on Spear Infantry.