The term Age is used to describe the periods of the Age of Empires series games. Advancement to an Age opens up new units and technologies for a civilization. Age of Empires and Age of Empires II have four Ages each; however, Age of Empires III and Age of Mythology have an extra fifth. In Age of Empires III, it can only be reached in a Supremacy-type game. In Age of Mythology, the fifth Age was introduced in The Titans. In all three Age of Empires games, including each expansion, the player is able to choose which Age to start from at the beginning of a game.