The history of the world as told through one hundred objects from the British Museum. This week Neil MacGregor, the Museum's Director, has been looking at the collapse of old regimes and the emergence of new powers from the Middle East to China. In today's programme, he describes how a powerful new state finds a dramatic way to help run its increasingly complex economy and trading networks - using coins. Croesus was a king in what is now Western Turkey and his kingdom was called Lydia. It's remarkable that over two thousand years later we still have an expression that celebrates his wealth. Neil MacGregor considers how money, in the form of coins, first came about and describes the (hugely complex) methods of creating them. And whatever happened to Croesus?