when people changed from trading in things like, for example, cows and wheat to using money instead, they needed things that would last a long time. they must still have a known value, and could be carried around. the first country in the world to make metal coins was called lydia. these first appeared during the 7th century bc, in the western part of what is now turkey. the lydian coins were made of a weighed amount of precious metal and were stamped with a picture of a lion. this idea soon spread to greece, the rest of the mediterranean, and the rest of the world. coins were all made to the same size and shape. in some parts of the world, different things have been used as money, like clam shells or blocks of salt.