Each borough is made up of several officially recognized smaller districts or quarters (). The number of quarters that form a borough varies considerably, ranging from two (
Friedrichshain-Kreuzberg) to fifteen (
Treptow-Köpenick). Most of Berlin's quarters are further composed of even smaller so-called (neighborhoods), officially called . The number of officially recognized neighborhoods in Berlin's quarters also varies greatly, ranging from two (
Kreuzberg) to many more in older quarters, for example nine in
Mitte, with many more unofficial neighborhoods and neighborships having formed over the decades. The quarters of Berlin and many of their neighborhoods typically have a historical identity as former independent cities, villages, or rural municipalities that were united in 1920 as part of the
Greater Berlin Act, forming the basis for the present-day city and state. Berliners often identify more with the quarter where they live than with the borough that governs them, and in larger or older quarters, the smaller neighborhoods have often become the defining social spheres for their residents. The quarters do not have their own governmental bodies, but for urban planning and statistical purposes, the quarters are officially recognized and further subdivided into statistical zones and (lifeworld-oriented regions). These areas correspond roughly, but not exactly, with the official and unofficial social and historical neighborhoods recognized by residents. When Greater Berlin was established in 1920, the city was organized into twenty boroughs, most of which were named after their largest component quarter, often a former city or municipality; others, such as
Kreuzberg and
Prenzlauer Berg, were named for geographic features. Minor changes to borough boundaries were made in 1938. After World War II, Berlin was divided into four sectors, with the Western sectors controlled by the United States, Britain, and France, and the Eastern sector controlled by the Soviet Union. In 1961, the
SED built the Berlin Wall to divide the city, effectively separating West Berlin from East Berlin and the rest of East Germany. Three new boroughs were created in East Berlin:
Marzahn was split off from
Lichtenberg in 1979,
Hohenschönhausen from
Weißensee in 1985, and
Hellersdorf from Marzahn in 1986. In 1989, the Berlin Wall fell, and the city was reunified. This marked the end of the Cold War and the beginning of a new era in Berlin's history. After reunification, Berlin underwent a process of rapid transformation, as the city worked to rebuild and modernize its infrastructure and economy. Many new businesses and cultural institutions were established, and the city became a center of creativity and innovation. By 2000, Berlin comprised twenty-three boroughs, as three new boroughs had been created in
East Berlin. Today Berlin is divided into twelve boroughs, reduced from twenty-three boroughs by Berlin's 2001 administrative reform. ==Boroughs==