Era
From Civilization Modding Wiki
The Era value is which era the game/scenario will start in. This value can be any of the Civilization IV eras that are defined in the file "CIV4EraInfos.xml" (found in your Civ4 directory/Assets/XML/GameInfo). The possible values are:
ERA_ANCIENT
ERA_CLASSICAL
ERA_MIDIEVAL
ERA_RENAISSANCE
ERA_INDUSTRIAL
ERA_MODERN
ERA_FUTURE
Original text by Dale on Apolyton Civilization Site and Civilization Fanatics Center from his "In depth look at the WBS file" thread.