Ore
Ore is one of the three basic resources in Heroes (along with Gold and Wood). Ore is needed for most buildings, and thus, it is vital to claim a source of ore as early in the game as possible. The primary source of ore is the Ore Pit, which brings its owner 2 units of ore per day. Typically basic resources can be found scattered around the adventure map in small amounts (5-10 units of ore per resource stack).
In Fortress, Castle, Necropolis and Stronghold towns you can also build the Resource Silo which will bring you 1 Wood and 1 Ore per day. Any hero equipped with the Inexhaustible Cart of Ore gives you 1 Wood every day.