 Age of Empires III is the first game in the series to introduce the " Home City " concept . The Home City functions as a second city , a powerhouse that is separated from the active game . It cannot be attacked or destroyed , although an Imperial Age upgrade called " Blockade " stops the player 's opponents from receiving Home City shipments . Similar to a role @-@ playing game character , the Home City is persistent between games , meaning that upgrades gained through separate games can be applied and stay applied for as long as that particular city exists . Multiple Home Cities can be created and maintained , although each supports only one civilization . 
