from Hang The Bankers:
Before the Renaissance, world money existed as precious metal coins or bullion. Caesars and kings hoarded gold and silver, dispensed it to their troops, fought over it, and stole it from each other. Land has been another form of wealth since antiquity.
Still, land is not money because, unlike gold and silver, it cannot easily be exchanged, and has no uniform grade.
In the fourteenth century, Florentine bankers (called that because they worked on a bench or banco in the piazzas of Florence and other city states), accepted deposits of gold and silver in exchange for notes which were a promise to return the gold and silver on demand. The notes were a more convenient form of exchange than physical metal. They could be transported long distances and redeemed for gold and silver at branches of a Florentine family bank in London or Paris.
Bank notes were not unsecured liabilities, rather warehouse receipts on precious metals.
Renaissance bankers realized they could put the precious metals in their custody to other uses, including loans to princes. This left more notes issued than physical metal in custody. Bankers relied on the fact that the notes would not all be redeemed at once, and they could recoup the gold and silver from princes and other parties in time to meet redemptions. Thus was born “fractional reserve banking” in which physical metal held is a fraction of paper promises made.
Despite the advent of banking, notes, and fractional reserves, gold and silver retained their core role as world money. Princes and merchants still held gold and silver coins in purses and stored precious metals in vaults. Bullion and paper promises stood side-by-side. Still, the system was bullion-based.
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