Foreign currency trading is not measured in length. However, the breadth and depth of foreign currency trading encompasses most of the world's currencies and if properly traded and understood can be used to make a large profit.
China's trading went all over the world using The Silk Road and many European traders who came from China, continued to spread Chinese goods even more.
Forex is a company that deals with foreign currency trading. Noble Trading is a New York based foreign currency trading company. There are many companies that deal in this business.