Berlin is the capital of the federal republic of Germany and it is both a city and a federal state. With over 3.4 million inhabitants the city-state is the biggest city in Germany, but it is only the third most densely populated community in Germany with 3.800 inhabitants per square-kilometre. Berlin is surrounded by the federal state of Brandenburg and together they form the metropolitan area of Berlin/Brandenburg with six million residents. The area of the city is 892km², with 38km in the north-south direction and 45km in the east-west direction. Three major rivers are found in the city proper: Spree, Havel and Dahme as well as several smaller ones and numerous lakes and forests.
Berlin was first mentioned in a document in 1237. Over the course of time the city was the seat of power and capital of Brandenburg, Prussia and the German Empire. The eastern part of Berlin was, since 1949, the capital of the democratic republic of Germany and after the German reunification it became the capital of all Germany.