If you want to understand how an old monetary system worked, the first place to look is the coins. They are durable and typically stored in secured locations, perfect for preservation. Yet, if you only study what survived, you’ll never get the full picture. You must also study the stuff that burned, decomposed and disintegrated. Imagine future historians studying the Great Recession by only looking at nickels and euros. They must examine online banking statements, read economic papers, research mortgage backed securities and junk bonds. “Coinage may have been only the very tip of the monetary iceberg,” Felix Martin concludes in Money: The Unauthorized Biography.