Finish an Era with a Village of 1000 Prosperity and at least 8 Mountain Patches within borders
Ambassadors. Have the Rock Giant acquaint himself with 2 Swamp and 2 Desert Ambassadors and the Swamp Giant grab 2 Desert and 2 Swamp Leaders. Our focus here, as with many level 3 developments, is Iron.
Once you have the required Giant proceed to create you mountain town. Place two mountains, leaving four spaces in between them, and then add a resource on a mountain’s lowest point; the village will set up in between.
Now proceed with the usual high yield tactic of Great Iron on danger spots. Try and use the mountains as Mineral, Animal, Mineral, Animal, Mineral. This way you can create six Iron generating in excess of 100 resources each - these tiles alone will drive three quarters of the required prosperity.