On a spring day more than 5,000 years ago in the Mesopotamian city of Ur, a foreign merchant sold his wares in exchange for a large bundle of silver.  He didn't want to carry the bundle home because he knew he'd be back in Ur again to buy grain at the end of harvest season.  Instead the merchant walked to the local temple, where valuables were often stored, and asked the priest to hold onto the silver for him.