The Medici Bank

Siege of Ferrera, Circa 1380
Welcome to 14th Century Italy, a land divided into various warring city-states, each completely independent from each other.
The problem with the system of city-states is that each city had it's own currency. This made it difficult to trade
So the Medici family began selling their Currency Conversion, in which they would charge a commission in exchange for doing foreign exchange.
Medici begin Foreign Exchange, Medici Bank Circa 1400
Venice, Jews used to avoid Usury, Circa 1400
In Venice, we use Jewish people to charge Interest for loans as when interest is charged by people of the same religion, it is considered a sin.
I am a Jew and I am here to charge interest for your recent loan
Very well then! I am a christian Venetian and I shall pay you the interest.
Hmmm, perhaps I can use foreign exchange as a way to give loans, using commission to bypass the prohibition of Interest!
Venice, Medici Bank begins operation, circa 1405
Hey! You don't need to talk to Jews to bypass Usury! How about I exchange your currency for florins, and I'll charge a little bit of Commission!
That sounds perfectly legal according to the teachings of the bible! Very well then!
Medici become rulers of Florence, 1434