Somewhere, I have some notes on an IMG sub-cult of Issaries that acts as bankers in the 14th century Italian & southern French mode. Initially, they issue letters of credit to merchants so that they don't have to cart money around. This only works between major cities in the interior of the empire where trade flrows are well enough understood that no money had to regularly pass between the branches. They have magic ledgers that allow each bank to see the other's ledgers. One cult hero invented double entry book keeping.
Then a hero of the cult comes up with the stage coach style money run to outlying areas. Fees are higher, but it supports the army, so everyone is happy.
Then another hero invents bank notes (initially through negotiable letters of credit). Fortunately, the moon falls before that goes very far. During the Monster Empire, an illuminatus should use this secret to cheat everyone in some region out of their hard currency.
Of course, the subcult is called Dafed and the high priest is Goldspan. The banks are usually called mints because no one knows what a bank is; the guards are spearmints.
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