If you don't want your enemies to be able to steal all your gold, you can leave some of it with a banker. You can access these funds from any of the cities in the game.
Depositing and Withdrawing
Banking is pretty straight forward. There is a Bank bar located in the center of every City page. This bar includes how much cash you have in your bank, three entry fields for how much you wish to move, one each for Gold Crowns (g), Silver Marks (sm) and Copper Pennies (cp), a C button that will clear any amount already in the fields, a Deposit, Withdraw and, if you're in a clan, a Donate button.
To deposit or withdraw, simply enter the amount you wish to transfer either way, and click the appropriate button. However, there is a small restriction. By default, you can only deposit 80% of your cash into your bank. There are City Upgrades which can increase this from 80% to 90%, so be sure to keep track of which cities have the best upgrade.
If you have more than the 10-20% required in your pocket when you open a city page, the difference will automatically be entered in to the deposit/withdraw fields and all you'll have to do is click the Deposit button.
There is a 1cp tax for each transaction that goes into the City's coffers. Note: Sometimes due to rounding, there will still be 1cp in the entry field after a deposit. At this point, if you click deposit again, the 1cp will just go to the city's bank, and not yours.
Donating to Your Clan
If you are a member of a clan, you will also have the option of donating money to your clan's bank. Donating to your clan can help out in a few ways. It will help them be able to stock shops in cities, and buy clan upgrades so that your clan's dominance can be felt around the world. The money you donate comes out of your bank, not your pocket, so keep that in mind.
To donate, simply fill in the entry fields with the amount you wish to transfer, and click the Donate button.
There is no minimum amount you have to donate, but you obviously can't donate more than you have in your bank at the time. And as any good clan leader will tell you, you can most definitely donate all of the coin in your bank.
You know you want to.
It's just the right thing to do.
There are 3 denominations of coinage in the game. The smallest are Copper Pennies(cp), the middle are Silver Marks(sm), and the largest are Gold Crowns(g).
100cp = 1sm
100sm = 1g
100g = A pretty good start.