Food is also used as upkeep for your army. The amount of food consumed by different units varies and can be found in the units page.
Food is gathered at farms, and can be plundered from enemy cities and barbarian camps. Merlin's Magical Boxes give out items that can be turned in for food and other items that will increase your ability to produce food.
Increasing food production
The farms in the fields around your cities produce food. When more fields are built into farms, your food production will go up. Increasing the level of the farms will also raise your food production.
Negative food income
When you have more soldiers than your farms can produce food for, you have a negative food income.
Always keep the food production higher then the upkeep, or ensure a high enough stock! Otherwise troops will just disappear!
The items Horn of Plenty, Horn of Bounty, and Horn of Majesty will decrease your troop upkeep by 50% for 8 hours, 24 hours, and 3 days respectively.