Frankfurt am Main is the largest city in the German state of Hesse and the fifth-largest city in Germany, with a 2008 population of 670,000. The urban area had an estimated population of 2.26 million in 2001. The city is at the centre of the larger Frankfurt Rhine Main Region which has a population of 5.3 million and is Germany's second largest metropolitan area. In English, this city's name translate as "Frankfurt on the Main". A large early tribe in the area was the Franks and in German "Furt" means a river crossing. Thus, in medieval times, "Frankfurt" meant the Franks' river crossing. Situated on the Main River, Frankfurt is the financial and transportation centre of Germany and the largest financial centre in continental Europe. It is the place of residence of the European Central Bank, the German Federal Bank, the Frankfurt Stock Exchange and the Frankfurt Trade Fair, as well as several large commercial banks. Frankfurt International Airport is one of the world's busiest airports, Frankfurt Central Station is one of the largest terminal stations in Europe, and the Frankfurter Kreuz (Autobahn interchange) is the most heavily used interchange in continental Europe. Frankfurt is the only German city listed as one of ten Alpha world cities.[2] Frankfurt lies in the former American Occupation Zone of Germany, and it was formerly the headquarters city of the U.S. Army in Germany, but what is left of that organization has moved out of Frankfurt to some more remote location. Among English speakers the city is commonly known simply as "Frankfurt", though Germans occasionally call it by its full name when it is necessary to distinguish it from the other (significantly smaller) "Frankfurt" in the state of Brandenburg, Frankfurt (Oder).