Defense of the Ancients (often referred to as DotA) is a custom scenario for Warcraft III: The Frozen Throne, based on the "Aeon of Strife" map for StarCraft. The objective of the scenario is to destroy the opponents' "Ancient", a heavily guarded structure in each corner of the map. Players use powerful units known as heroes, and are assisted by allied heroes and AI-controlled fighters called "creeps". As in role-playing games, players level up their hero and use gold to buy equipment during the mission.