 Bremen is the largest city on the River Weser, the longest river flowing entirely in Germany, lying some upstream from its mouth into the North Sea, and is surrounded by the state of Lower Saxony.A commercial and industrial city, Bremen is, together with Oldenburg and Bremerhaven, part of the Bremen/Oldenburg Metropolitan Region, with 2.5 million people.Bremen is contiguous with the Lower Saxon towns of Delmenhorst, Stuhr, Achim, Weyhe, Schwanewede and Lilienthal.