A treasury is a side's total accumulated Shmuckers. A treasury is not a physical storehouse of gold or coins, but is a construct of natural Moneymancy common to all sides. At the start of a turn, the income of all cities and other sources of Shmuckers is paid into the treasury, and the total upkeep of all units on a side is paid out of the treasury, automagically. All commanders on the side can sense its current value.
Unlike a purse, there is no upper limit to the amount of Shmuckers a treasury can hold.
Should a side's capital be captured, the value of the Shmuckers in the side's treasury is transferred to the treasury of the side which claims the capital site.
Charlescomm estimates that the average Erfworld treasury is about 360,000 Shmuckers. A side with 3,000,000 Shmuckers would be considered wealthy.Erf-b3-p152 Bonnie guessed Charlescomm itself to have a treasury of 20 million, though that guess was far off the mark.