Which preposition to use with flensburg

to Occurrences 1%

In this situation of affairs, knowing that Denmark would not consent to any other lineindeed, not knowing whether the German Powers would concede any other linethe Prussian Plenipotentiary said that he was ready to recommend to his Government a line which should proceed from the north of Flensburg to Tondern, but that he was not authorized to propose that line in the name of his Government.

Which preposition to use with  flensburg