Have you ever looked at your finances on ikariam and wondered where all your hard earned gold is going?
Heres a basic breakdown:
1. Workers cost money (all that slave labour down the mines and at the forests does actually cost some)
2. Researchers (I know they get to play with crystal all day AND they get paid!)
3. Don't forget your military, they do like to be paid for putting their butts on the line for you!
On the plus side though guys, spies don't cost any upkeep!
Another general point that i've taken from a website:
Units on missions or being relocated from one city to another cost twice the upkeep.
If you have several colonies, the amount of upkeep shown in the income overview is divided between your towns dependent on the percentages of the total amount of citizens per town you have, not on the amount of stationed troops and ships. As cities don't have their own gold reserves and all costs are paid out of your gold coffer, this of course only makes your bookkeeping harder to read, rather than offering any insights into where your real costs per city come from.
Finally for a little extra info check out:
http://ikariam.wikia.com/wiki/Upkeep