From the longer German Wikipedia page [1]

The City Archives Frankfurt (Oder) is the archives of the City of Frankfurt (Oder) in the state of Brandenburg, Germany.

The oldest existing archival directory in Frankfurt dates from 1546. In 1822 the archive was rearranged by Heinrich Bardeleben and made accessible to historical people. In 1890 the archive was moved from the town hall to the sacristy of the Franciscan monastery church and Adolf Gurnik was appointed as the first archivist. Further rearrangements took place, and towards the end of the Second World War, outscritions were made to the east. After the conquest of the Red Army, many of the documents deposited in the city were lost by firefighting.

In the spring of 1946, Elfriede Schirrmacher began to save the remaining stocks and to reunite them. In 1962 62 archival records from Poland were returned to the Frankfurt Archive. In 1976, the archive building was moved to Collegienstrasse and the last director, Ralf-Rüdiger Targiel (* 1953), took over the management.

The website, in German, is [2].