Geography and urban development of Dresden past 60 years has made Dresden the fourth largest urban area in Germany after Berlin, Hamburg, and Cologne. The most important river in Dresden is the Elbe river, the only navigable body of water to flow through the city. There are also a number of tributaries such as the river Weißeritz. The nearest German cities are Chemnitz (80 km to the southwest), Leipzig (100 km to the northwest) and Berlin (200 km to the north). The Czech capital Prague is about 150 km to the south; the Polish city of Wrocław is about 200 km to the east. There are
Accession of Hamburg to the German Customs Union (Zollverein) form a wider more powerful entity. The states which joined fought vigorously against any impairment of their full sovereignty. Hence each member had a veto and the union was not permanent, but had to be renewed after 12 years. Each member sought its own economic advantage. Accordingly, the accession of any of the Hanseatic cities of Hamburg, Bremen or Lübeck would have to be on condition that accession served the city's own advantage. A pre-condition of such advantage was that their territory touched directly with that of the Customs Union, which only happened for Hamburg after 1854, when Hanover joined.