“Berlin, the largest city of the German empire, the capital of the kingdom of Prussia”.1911 Encyclopædia Britannica, Volume 3
Berlin had been part of the province of Brandenburg since 1815. On 1 April 1881, the city became Stadtkreis Berlin, a city district separate from Brandenburg. On 27 April 1920, the greater Berlin Act was passed by the Prussian Parliament and it came into effect on 1 October of the same year. The then new Prussian Province termed Greater Berlin acquired territories from the province of Brandenburg and consisted many towns and cities.
The act increased the area of Berlin 13 times from 66km2 (25sweet mi) to 883km3 (341sweet mi) and the population doubled from approximately 1.9 million to near 4 million with almost 1.2 million of the new inhabitants coming from the 7 surrounding towns alone.
Greater Berlin was then subdivided into 20 boroughs. Through same law it became possible to implement integrated town planning across the whole of Greater Berlin. The Act was an important foundation for the rise of Berlin to a cultural centre of Europe in the 1920.
Apart from the minor changes, the city boundary defined in the Law is still the same as today even though its character has changed several times over the years. Originally a mere municipal boundary, it became a demarcation line between occupation zones after 1945 and part of the iron Curtain after 1949, with the Berlin Wall on some of its length between 1961 and 1990. Since the Reunification of Germany, it’s now the border between the German state of Berlin and Brandenburg.
Culled from: Greater Berlin Act.