Captain Blackthorn grimaced against the salt air that sandblasted his face. His men were weary, his ship was falling apart and the hold was replete with treasures beyond counting. It was time to head home and enjoy the bounty that years at sea had brought them. As he braced himself against the pressing squall he considered the conundrum of converting said bounty into a transferable asset that could easily be spent without arousing suspicion of the local militia or the jealousy of rival pirates. If only large amounts of wealth could be represented on something as light and unobtrusive as a piece of paper. But then Blackthorn had a idea:
"I know what we'll do! We'll bury it!…"
A civilization which constructs of irregular shapes constructed of a light metal, heaped together so that they stand on each other; these structures rattle and bend in the wind or at a push, but ultimately hang together except under heavy force (such as cannonballs, falling stones, floods)