Claim: Berlin's important industries include clean tech.

Berlin -LRB- -LSB- bəɹˈlɪn -RSB- , -LSB- bɛɐ̯ˈliːn -RSB- -RRB- is the capital and the largest city of Germany as well as one of its 16 constituent states . With a population of approximately 3.7 million , Berlin is the second most populous city proper and the seventh most populous urban area in the European Union . Located in northeastern Germany on the banks of the rivers Spree and Havel , it is the centre of the Berlin-Brandenburg Metropolitan Region , which has roughly 6 million residents from more than 180 nations . Due to its location in the European Plain , Berlin is influenced by a temperate seasonal climate . Around one-third of the city 's area is composed of forests , parks , gardens , rivers , canals and lakes .   First documented in the 13th century and situated at the crossing of two important historic trade routes , Berlin became the capital of the Margraviate of Brandenburg -LRB- 14171701 -RRB- , the Kingdom of Prussia -LRB- 1701 -- 1918 -RRB- , the German Empire -LRB- 1871 -- 1918 -RRB- , the Weimar Republic -LRB- 1919 -- 1933 -RRB- and the Third Reich -LRB- 1933 -- 1945 -RRB- . Berlin in the 1920s was the third largest municipality in the world . After World War II and its subsequent occupation by the victorious countries , the city was divided ; East Berlin was declared capital of East Germany , while West Berlin became a de facto West German exclave , surrounded by the Berlin Wall -LRB- 1961 -- 1989 -RRB- and East German territory . Following German reunification in 1990 , Berlin once again became the capital of all-Germany .   Berlin is a world city of culture , politics , media and science . Its economy is based on high-tech firms and the service sector , encompassing a diverse range of creative industries , research facilities , media corporations and convention venues . Berlin serves as a continental hub for air and rail traffic and has a highly complex public transportation network . The metropolis is a popular tourist destination . Significant industries also include IT , pharmaceuticals , biomedical engineering , clean tech , biotechnology , construction and electronics .   Modern Berlin is home to world renowned universities , orchestras , museums , entertainment venues and is host to many sporting events . Its urban setting has made it a sought-after location for international film productions . The city is well known for its festivals , diverse architecture , nightlife , contemporary arts and a high quality of living . Since the 2000s Berlin has seen the emergence of a cosmopolitan entrepreneurial scene .