Berlin/Brandenburg Metropolitan Region in the context of "Potsdam"

The Rhine-Main Metropolitan Region, often simply referred to as Frankfurt Rhine-Main, Frankfurt Rhine-Main area or Rhine-Main area (German: Rhein-Main-Gebiet, Frankfurt/Rhein-Main or FrankfurtRheinMain, abbreviated FRM), is the third-largest metropolitan region in Germany after Rhine-Ruhr and Berlin-Brandenburg, with a total population exceeding 5.9 million. The metropolitan region is located in the central-western part of Germany, and stretches over parts of three German states: Hesse, Rhineland-Palatinate, and Bavaria. The largest cities in the region are Frankfurt am Main, Wiesbaden, Mainz, Darmstadt, Offenbach, Worms, Hanau, and Aschaffenburg.

The polycentric region is named after its core city, Frankfurt, and the two rivers Rhine and Main. The Frankfurt Rhine-Main area is officially designated as a European Metropolitan region by the German Federal Ministry of Transport, Building and Urban Affairs and covers an area of roughly 13,000 square kilometers (5,000 sq mi).

Berlin is the capital of Germany, as well as its largest city by both area and population. With 3.7 million inhabitants, it has the highest population within its city limits of any city in the European Union. The city is also one of the states of Germany, being the third-smallest state in the country by area. Berlin is surrounded by the state of Brandenburg, and Brandenburg's capital Potsdam is nearby. The urban area of Berlin has a population of over 4.6 million, making it the most populous in Germany. The Berlin-Brandenburg capital region has around 6.2 million inhabitants and is Germany's second-largest metropolitan region after the Rhine-Ruhr region, as well as the fifth-biggest metropolitan region by GDP in the European Union.

Berlin was built along the banks of the Spree river, which flows into the Havel in the western borough of Spandau. The city includes lakes in the western and southeastern boroughs, the largest of which is Müggelsee. About one-third of the city's area is composed of forests, parks and gardens, rivers, canals, and lakes.

Brandenburg, officially the State of Brandenburg (see Names), is a state in northeastern Germany. Brandenburg borders Poland and the states of Berlin, Mecklenburg-Vorpommern, Lower Saxony, Saxony-Anhalt, and Saxony. It is the fifth-largest German state by area and the tenth-most populous, with 2.5 million residents. Potsdam is the state capital and largest city. Other major towns are Cottbus, Brandenburg an der Havel and Frankfurt (Oder).

Brandenburg surrounds the national capital and city-state of Berlin. Together they form the Berlin/Brandenburg Metropolitan Region, the third-largest metropolitan area in Germany. There was an unsuccessful attempt to unify both states in 1996, and the states still cooperate on many matters.

The idea of unifying the German states of Berlin and Brandenburg has gained particular notoriety since German reunification.