The ancient economy's use of credit and finance was more sophisticated than often assumed. Roman banking (the argentarius or mensarius) provided loans, deposits, and money-changing services. Partnerships (societates) allowed wealthy investors to pool resources for large commercial ventures.

The financial instruments available to ancient merchants — bottomry loans (loans on the security of a cargo at sea, forgiven if the cargo was lost), letters of credit, bills of exchange — allowed complex commercial transactions across distances that would otherwise be impossible. The bottomry loan in particular was sophisticated: it transferred maritime risk from merchant to banker, allowing traders to undertake voyages they couldn't otherwise have financed.

Interest rates in the ancient world were high by modern standards — typically 8-12% per annum for secured loans, much higher for unsecured or maritime credit. The Roman legal prohibition on charging interest (usury) to fellow citizens was repeatedly circumvented through legal fictions. The actual market for credit was not inhibited by moral prohibitions in practice.

The Sulpicii archive, a collection of wax tablets from Puteoli (the main port for Roman trade with the East), gives us the most detailed picture of commercial banking practice in the 1st century AD. The tablets document loans, auctions, and storage agreements in the context of long-distance maritime trade. They show a financial system considerably more sophisticated than the 'barter economy' that some older scholarship imagined.