Banks would issue an instrument shows what you were good for; think a bearer bond or even money order, if you like. They write a letter saying what you’re good for, but you still had to get that letter from your main bank.
This is actually how many of the Crusader Orders started as; the Knights Templar would issue you a letter of credit for your journey to the holy land. The disruption of this credit system/revenue stream was one of the major causes of the Crusades.
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