Mitte is the first and most central borough of Berlin. It was created in Berlin's 2001 administrative reform by the merger of the former districts of Mitte proper, Tiergarten and Wedding; the resulting borough retained the name Mitte. It is one of the two boroughs (beside Friedrichshain-Kreuzberg) which comprises former West and East Berlin districts. Mitte encompasses Berlin's historic core and includes some of the most important tourist sites of Berlin like Museum Island, Brandenburg Gate, Unter den Linden, Potsdamer Platz, the Reichstag and Berlin Hauptbahnhof, most of which were in former East Berlin.
Note that when Berliners speak of Mitte, they usually refer to the smaller locality and not to the larger borough.