Age of Empires (often abbreviated to AoE) is a history-based real-time strategy video game released in 1997. Developed by Ensemble Studios and published by Microsoft. Ensemble was still an independent company, later acquired by Microsoft. The game uses the Genie, a 2D sprite-based game engine. The game allows the user to act as the leader of an ancient civilization by advancing it through four ages (the Stone, Tool, Bronze, and Iron Ages), gaining access to new and improved units with each advance. It was later ported to Pocket PCs with Windows, resulting in a version very similar to the PC game.