A city park fully contained within a private cemetery — weird! From the Parks Department's website:
On April 28, 1863, the City of New York purchased the land for this park from the Trustees of St. Patrick's Cathedral and granted Parks jurisdiction over it. The land transaction charter stated that Parks would use the land as a burial ground for soldiers who fought for the Union during the Civil War (1861-65) and died in New York hospitals. Parks is responsible for the maintenance of the Civil War monument, the statuary, and the surrounding vegetation. Twenty-one Roman Catholic Civil War Union soldiers are buried here. The last burial took place in 1909.I had never been to this part of the cemetery before, but the four statues at the base of the monument (individual photos about halfway down this page) looked very familiar. It turns out that they're identical (albeit with some missing pieces) to the figures on the Soldiers’ Monument at Green-Wood Cemetery (photos: 1, 2, 3, 4), as well as other Civil War monuments around the country.