An era is a period of time in Civilization IV and its expansions. Civilizations can progress to a new era by researching new technologies. The eras in the game are as follows: * The Ancient Era is the first time period of the game. * The Classical Era is the second time period of the game. * The Medieval Era is the third time period of the game. * The Renaissance Era is the fourth time period of the game. * The Industrial Era is the fifth time period of the game. In this era, the appearance of Workers and roads changes. * The Modern Era is the sixth time period of the game. * The Future Era is the seventh and final time period of the game.