When your city is under attack, wounded troops will be sent to the Asclepeion and ward instead of dying, except when the number of wounded troops exceeds the maximum Asclepeion capability.

Far less time and fewer resources are needed to heal wounded troops as opposed to training troops. Therefore, upgrading Asclepeion and Wards is the most effective way to reduce troops losses.

Special Note: your marching troops outside of your city will not be sent to Asclepeions if you are attacked.