Since Age of Empires debuted in 1997, the series has grown to become one of the pillars of real-time strategy gaming. Its success is in part due to the way the series has shifted historical periods. The first game covers antiquity, from the Stone Age to the Roman Empire. Meanwhile, Age of Empires II focuses on the medieval era. And 2005's Age of Empires III is about the era of European exploration and colonization.