The Bibliothèque nationale et universitaire (BNU) is, with its collection of more than 3,000,000 titles, the second largest library in France after the Bibliothèque nationale de France. It was founded by the German administration after the complete destruction of the previous municipal library in 1871 and holds the unique status of being simultaneously a students' and a national library. The Strasbourg municipal library had been marked erroneously as "City Hall" in a French commercial map, which had been captured and used by the German artillery to lay their guns. A librarian from Munich later pointed out "...that the destruction of the precious collection was not the fault of a German artillery officer, who used the French map, but of the slovenly and inaccurate scholarship of a Frenchman."
Try to answer this question if possible (otherwise reply "unanswerable"): In what year did a French map maker accidentally mark the library as "City Hall"?
unanswerable