 The units of Age of Empires III are based , as in previous iterations of the game , around military classes of the historic time period . The player controls a variety of civilian and military units , and uses them to expand and develop their civilization , as well as wage war against opponents . The base unit of a game is the settler , responsible for gathering resources and constructing buildings , in order to improve the economy of the civilization . The number of units a player can control in a scenario is limited by a " population limit " , a common real @-@ time strategy game mechanic . Houses and town centers raise the starting limit , to a maximum of 200 , while each unit that is produced increases the population count . Basic units such as settlers and infantry count as 1 , but others , including most cavalry and mercenary infantry count as 2 . More powerful units , especially artillery or mercenary cavalry , can count for a population as high as 7 . Native warriors , explorers , tamed and grazing animals , hot air balloons and warships do not count towards the population limit , but generally have a build limit , allowing the player to deploy only a certain number of those specific units at a time . 
