I've seen many factions (such as the celts and greeks) got spearmen as main frontline infantry, while other factions such as the Romans got the swordsman as standard infantry.
In this case I would like to know what are the main differences and bonuses for the spearmen and the swordsmen.
I know the spearmen got 3x bonus against calvalry, but I've seen in many games a group of spearmen being in some cases more effective than the swordsmen against other units.
How should I properly use them individually?