Hammers, , are one of the three basic economic inputs found in Civ 4. Hammers are produced by tiles when they are worked by population in a city. See the article on production for more info.
Hammers are produced inherently by these types of terrain:
Tile improvements Edit
Additional hammers may be generated by these tile improvements:
Some resources generate hammers. These resources add 1 hammer to their tile even before they are improved, and they generate more hammers if improved with the proper tile improvement:
Some resources add hammers only when they've been improved with the particular improvement which unlocks the resource: