Okay, we’re not talking about mountain as in the Rockies.
It was more of a hill, a 60-foot incline called Mount Pitt about where Grand and Pitt Streets cross today.
For Manhattan at the time, this “mount” was a high point, affording incredible vistas New Yorkers would kill for now.
Let a book published in 1879 by a descendant of the man who made his home on the hill give the details (and then check out the country road–like view in the NYPL Digital Collection illustration:
“Upon this fine site still, though graded down very much, the highest point of that part of the city, which then commanded a magnificent prospect, extending on the east beyond Hellgate, on the west over the city and the bay to the shores of Staten Island and New Jersey, and on the south over the East River and the heights of Long Island. . . .”
In pre-Revolution days, it was the location of a town home and gardens built by Judge Thomas Jones, hence why Mount Pitt is also known as Jones Hill.
During the war, colonists constructed a large redoubt on Mount Pitt called Jones Hill Fort.
Leveled after the war, Mount Pitt still exists in a way: fieldstone taken from it in the 1820s was used to build St. Augustine’s Church, on Henry Street.
Here’s Grand and Pitt Streets today: flattened out and a bit dreary. The current highest point in Manhattan lies several miles north.