Akinai (Civ3)/Civilopedia

As cities grew, their internal economies became more complicated. People became specialists, some primarily producing grain, some pottery, 
some bricks, etc. A system of barter developed, so that one individual's wares and services could be exchanged for those of another. Gold 
and silver were widely used in such transactions, but the pieces needed to be weighed and tested for purity each time they changed hands. In 
600 BC, the Lydians found a way around this problem. They began the practice of shaping electrum, an alloy of gold and silver, into pieces 
of predetermined weight and purity, stamped with an official symbol. This idea caught on, and within 50 years all the important trading centers 
of the world had adopted similar practices.