Commerce () is a one of the three basic economic inputs found in
Civilization IV. It is produced by trade routes, and by tiles
when they are worked by population in a city. See the article on
production for more info. Commerce should not be mistaken for
gold (). Gold is produced from commerce (if slider settings
indicate that), and gold is also produced by certain buildings.
Commerce is produced only by tiles and trade routes. Commerce is
produced inherently by the following types of terrain: Tile
Improvements Edit Commerce is generated by these tile
improvements: Many resources generate commerce. Some resources
add commerce to their tile even before they are improved: Many
resources add commerce only when they've been improved with the
particular improvement which unlocks the resource: