Trade in Civilization Revolution is tied to gold and science production. Trade can be either gold or science depending on what mode a city is placed in. It appears as an icon on the map in sea and desert squares as a circle with two arrows curved toward each other. Trade is affected by a civilization's abilities, form of government, wonders, and buildings. It is also affected by certain technology upgrades, such as Currency. Wine is the only resource which provides trade rather than gold, science, or culture.