Age of Empires requires the player to develop a civilization from a handful of hunter-gatherers to an expansive Iron Age empire. To ensure victory, the player must gather resources in order to pay for new units, buildings and more advanced technologies. Resources must also be preserved, as no new resources become available as the game progresses, meaning if you cut a tree down, the tree will not grow back. Twelve civilizations are available, each with individual sets of attributes, including a varying number of available technologies and units. Each civilization has technologies unique to them, so that no civilization possesses all the technologies possible within the game. A major component of the game is the advancement through four ages. These are the Stone Age (Mesolithic/Paleolithic), Tool Age (Neolithic/Chalcolithic), Bronze Age and Iron Age. Advancement between ages is researched at the Town Center and each advancement brings the player new technologies, weapons, and units.