Your Acropolis is the only truly safe place in the land of Hellas. Hide your Units in the Acropolis to protect them. Your recovered Resources will be automatically stored there. The number of Units you can hide is unlimited, but the amount of Resources that can be kept in the Acropolis depends on its Upgrade level. To view the amount of protected Resources, go to the Acropolis and click the "Info" tab. To view the number and type of hidden Units (Light Infantry, Heavy Infantry, Phalanx, and Cavalry), go to the Acropolis and open the "Units in Acropolis" tab.
In case of an enemy attack, the Units hidden in the Acropolis will not be involved in the battle and your Resources stored there will remain untouched. Never leave your Offensive Units vulnerable when not in use! Offensive Units have been trained only in the art of attack, and as such are unable to defend your City from enemies.
Let it be known that Spartans do not run from the battlefield - they simply go to the Acropolis to fight another day!