How and when do Troops desert?
On occasion, you may notice that a portion of your Troops have gone missing. If your City runs out of Food, your Troops may begin to desert. Troops can desert from Marches as well as from within your City Walls, so it's important to make sure your Troops stay fed at all times!
To check for Troop desertion, open your in game Messages to the Reports tab and click on the link that says View City Reports:
If you have experienced Troop Desertion you will be able to see the date and time they deserted: