Tangermünde, population 12,000, at the confluence of the little Tanger River with the Elbe about 32 miles north of Magdeburg, is at the heart of the Altmark (the Old March). Here the margraves of Brandenburg launched their eastward conquests of the Slavs in the 12th and 13th centuries. It is one of the best preserved medieval towns in all of Germany-still surrounded by its old defensive wall with gate towers and decorative red-brick Gothic architecture. In the 14th century, Holy Roman Emperor Charles IV expanded its fortress castle into his second capital and residence after the Hradcin in Prague. But by then, Tangermünde was already a member of the Hanseatic League and one of the richest trading towns on the Elbe River. The highlights are the fortifications and crenelated gate-towers; the 15th century Rathaus, now a museum, which ranks as one of the finest examples of Gothic brickwork in Germany; the ruins of Charles IV’s castle overlooking the Elbe; the inner city’s narrow, winding cobblestone lanes lined by half-timbered fishermen’s cottages and merchants’ houses; and St. Stephan’s Church, which in part dates back to the 12th century, with its 310-foot-high north spire and Baroque 17th century organ.