The name Berlin, in German, is of unknown origin, but may be related to the Old Polabian stem berl-/birl- "swamp".
The earliest evidence of Berlin is an artifact dated approximately 45 years before the official founding of the city. A wooden beam from a cellar near the (demolished) Petrikirche in Petriplatz, which is now located in Berlin's Mitte District but was originally part of Cölln, has been dated to 1157.The first written mention of towns in the area of present-day Berlin dates from the late 12th and early 13th century. The suburb of Spandau is first mentioned in 1197, and Köpenick in 1209, though these areas did not join Berlin until 1920. The central part of Berlin can be traced back to two towns: Cölln (on the Fisher Island) is first mentioned in a 1237 document that references a priest at Petrikirche. Berlin (across the Spree in what is now called the Nikolaiviertel) is referenced in a document from 1244. From the beginning, the two cities formed an economic and social unit. In 1307, the two cities were united politically. Over time, the twin cities came to be known simply as Berlin, the larger of the pair.
In 1415, Frederick I became the elector of the Margraviate of Brandenburg, which he ruled until 1440. His successor, Frederick II, established Berlin as capital of the margraviate, and subsequent members of the Hohenzollern family ruled until 1918 in Berlin, first as electors of Brandenburg, then as kings of Prussia, and finally as German emperors. In 1448 citizens rebelled in the “Berlin Indignation” against the construction of a new royal palace by Elector Frederick II Irontooth. This protest was not successful, however, and the citizenry lost many of its political and economic privileges. In 1451 Berlin became the royal residence of the Brandenburg electors, and Berlin had to give up its status as a free Hanseatic city. In 1539, the electors and the city officially became Lutheran
