The extension of purchasing power based on trust in a future payment — the claim side of the debt relationship and the social mechanism through which promises to pay have been made tradeable, circulated as near-money, and used to build everything from Mesopotamian grain networks to global capital markets.
In the ancient city of Ur, a merchant needed grain before the harvest came in. He did not pay with coins. He made a promise, pressed into wet clay, that he would deliver silver at a future date. The lender accepted the promise. Tablets like this are among the earliest surviving evidence for credit: promises to pay, recorded before coins were common. Not a loan in the modern sense. A trust relationship made legible. What civilization built on top of that clay tablet is the entire financial system: not money first and credit after, but credit first, as the promise that money was eventually invented to settle.