see also Worker Actions (Advanced) Irrigate (I) Increases food output. Build Mine (M) Increases shield output. Build Road (R) Increases commercial output and speeds movement. Build Railroad (R) Increases irrigation or mine output, and provides unlimited movement. Plant Forest (N) Adds a forest to a square. Clear Forest (Shift-C) Removes forest and sends shields to nearest city. Clear Wetlands (Shift-C) Removes jungle or marsh. Clear Damage (Shift-C) Removes pollution, including fallout from a volcanic eruption, and craters. Build Fortress (Ctrl-F) Increases a square's defensive value by 50%. Build Barricade (Ctrl-F) Turns Fortress into Barricade, doubling the square's defensive value. Build Colony (B) Colonies are built atop tradable resources. If connected to a city, a colony provides the resource to that city.