This is the 1099th most frequent Dutch word.
historische
"Historische" means "historical" in English.
In this sentence, 'historical' (historische) describes an attribute of the city, emphasizing its historical significance.
De historische stad had veel monumenten.
The historic city had many monuments.
Here, 'historical' specifies the nature of the document as something from or significant to history.
Het historische document werd in het museum bewaard.
The historical document was kept in the museum.
In this context, 'historical' describes the day as notable in history.