Irrigation is an economic upgrade featured in Age of Empires. This technology can be researched at the Market for 300 food and 100 wood once the player reaches the Iron Age and is the last upgrade that enhances farming productivity. Once researched, the total amount of Food available on a Farm increases by 125 points.
"One of the key steps in the agricultural revolution was understanding and managing irrigation. Observation of the natural world revealed eventually the relationship between planted seeds, good soils, sunlight, water, and resultant crops. Large- scale irrigation in both Mesopotamia and Egypt turned the rich but arid soils near the rivers into rich farmlands and made possible the rise of the great civilizations on earth. Building the dams and channels to irrigate these lands required sophistication of government, construction, and engineering not seen previously in any society."