Loot
Looting is an attack type that allows your Thieves to loot unprotected gold and Food, Weapons, Armor, War Machines, Scrolls, Maps and Artifacts. The greater the % of your thieves the better the chance to succesfully loot the enemy. The enemies' Rangers, Assassins and Thieves defend against looting. Vaults protect some gold from looting as well. Guard Towers double the covert defense of some of their Rangers.
Gold you could loot in 1 turn = # of Thieves x Thieves % x 2.5
PLUS if you have mages, 1 mage will loot for each 1 thief you have, except at only x 1.25 instead of x 2.5
Mage numbers and % do not have any impact on whether you will successfully loot though, only how much gold you can get.
EG 1: 15,000 thieves 500% + 10,000 mages 1000% = 18.75M + 12.5M = 31,250,000
EG 2: 300,000 thieves 400% + 300,000 mages 1000% = 300M + 375M = a whopping 675,000,000