International trade has one brutal problem: the seller wants the money before letting go of the goods, and the buyer wants the goods before parting with the money. Across an ocean, with no shared courts and no trust, that standoff kills deals. The letter of credit (LC), a device Italian merchant banks (the Bardi, Peruzzi and Medici) refined in the 14th–15th centuries, solves it by swapping the buyer’s promise for a *bank’s* promise.