Why is a "thing" called "东西" and not "南北"?
There were two large markets in ancient Chang'an (长安/長安) city of the Tang (唐) dynasty, one called east market (东市/東市) and the other one called west market (西市), gradually people perfer to say to buy east and west (去买东西/買東西) rather than to buy goods in east and west market (去东西市购买商品/去東西市購買商品). The new business district West Market of Great Tang (大唐西市) has reconstructed on the old site of the ancient west market in Xi'an Shaanxi (陝西西安/陕西西安) today.