Unlocks the Builder ability to construct the Great Wall, unique to China.

+1 Food, +2 Gold. Provides an increase to Defense. Enemy military units get -2 Strength for each adjacent Great Wall. +2 Culture for each adjacent Great Wall. +2 Gold for each adjacent Great Wall after researching 'Castles' Technology. Built on tiles adjacent to the builder. Must be built in a line along the borders of your empire. Can be built on Mountain, Forest or Swamp tiles. Can only be pillaged (never destroyed) by natural disasters.

Once Buttress is unlocked it can also be built on Floodplains.

+2 Culture from each adjacent Great Wall tile, requires Masonry.
+2 Gold from each adjacent Great Wall tile, requires Castles.