When the Roman emperor Constantine struck off a new gold coin, he expected it to give good, durable service. And the extra-durable solidus did - about 700 years' worth. Modern monetary systems have a somewhat shorter shelf life.

That the current monetary system may not last for the ages was underscored the other day by Kuwait's decision to uncouple its dinar from the US dollar. For years, the two had been lashed together as a preliminary to the projected creation of a common Persian Gulf currency.