Berlin grew out of the historical city centre, the Nikolai quarter and its adjacent town of Cölln, both situated along the River Spree. It expanded its territories with areas such as Dorotheenstadt and Friedrichstadt. The creation of Greater Berlin in 1920 incorporated many former independent towns and municipalities such as Spandau, Charlottenburg and Köpenick.
Today, the urban environment of the metropolis also spreads to parts of Brandenburg and Potsdam. The decentralised development has resulted in a plethora of sights in Berlin – not just in the centre of the city, but also in the outlying boroughs. For various reasons among the world's most recognized symbols of Berlin are the Brandenburg Gate and its tallest landmark, the Berlin TV tower in Mitte.