Through the game you and your opponents will race to discover ever more powerful technologies, which enhance your own civilizations while menacing those of each other. A few advances provide immediate benefits, such as making new actions available to your units; many introduce new units or buildings you can construct; and most are also gateways to further technology. Beware that some advances also make things obsolete. While obsolete units merely become impossible to make — leaving the ones you have already made intact — obsolete buildings are immediately sold, and obsolete wonders lose their effect. Worse yet, your wonders can be obsoleted by an advance made by another player!