Picture yourself carrying silver across a medieval market square. Not a romantic image: you are sweating through your coat, mentally converting three coinages at once, and acutely aware that the man behind you has been following you since the cloth stalls. So you don't carry the silver. You leave it with someone whose ledger you trust, take a written note instead, and walk home lighter. That decision, repeated thousands of times across a handful of specific cities, is where deposit banking begins. Not in the great open ports, for all their noise and tonnage. In the walled ones.

The puzzle is genuine. Venice and Genoa were processing more commercial volume than anywhere in Europe across stretches of the twelfth and thirteenth centuries, probably by a considerable margin. Yet the institutional machinery of deposit banking, the written ledger transfer, the claim on a named account that could be assigned to a third party without physically moving coin, crystallised first in places like the fairs of Champagne and later in cities such as Barcelona and Bruges. Volume alone didn't produce the institution. That should bother anyone who assumes finance simply follows trade.