I recall having read a short story, most likely in the '90s, about a man in medieval Italy, depositing a modest sum in pure gold with a bank, for a period of a hundred years. He also gives some predictions and directions on how to invest it.
A century later, a similar man appears, not withdrawing his accumulated wealth, but reinvesting it, strengthening the contract, and again making predictions.
This goes on until the 20th century. It is by then the largest fortune in the world by far, unbeknownst to all but the select few managing it. Wars have been fought over it, ostensibly for other reasons but secretly between different factions managing the fortune. I think it's even hinted at that both World Wars were fought because of the fortune.
The man appears and wants to liquidate his assets, because he needs the funds to
build a time machine and go back to medieval Italy to deposit the gold that started it.