Like many typical names from Eastern Germany, Berlin has its origin in the Slavic language, more precisely in Old Polish. Thus, the name Berlin is composed of “birl-“, or “berl-” for swamp or morass, and the suffix “in” typical of place names.
Berlin is, therefore, according to its name, the place in the swamp.
This may come as a disappointment to many Germans who thought Berlin came from the German word for bear (”Bär”). Since it is pronounced similarly to the “Ber” in Berlin. The Berlin coat of arms also features a bear. No wonder this assumption is so persistent.