frankfurt, officially frankfurt am main (; hessian: "frangford am maa", "frank ford on the main"), is one of the biggest cities in germany. the city of frankfurt has a population of 700,000. the metropolitan area, called rhine-main after its two biggest rivers, has over four million people. frankfurt is an important centre for traffic and for the financial business. the frankfurt international airport is the largest in germany, and one of the largest in the world. frankfurt's train station is one of the largest, and its highway crossing is the centre of germany's street network. frankfurt is the seat of the european central bank, the german federal bank (bundesbank) and of the biggest german banks, and it has an important stock exchange where shares of german companies are traded.