Detailed photograph showing the final stages of construction in early 1902 on the Metropolitan Museum of Art.

The Fifth Avenue addition to the original 1874 Calvert Vaux building was designed by architect Richard Morris Hunt and features a grand staircase with Corinthian columns. Along the cornice above the columns sit pyramids of rough-hewn limestone slabs, originally intended to serve as the basis for four sculptural groups. But the sculptures were never carved out and the massive stacks of limestone still remain on the cornice! 

There are theories as to why this is. First, the architect died in 1895 and never saw the building completed. Additionally, the economic depression of 1893-7  led to Hunt's chosen material, marble, being substituted for the cheaper limestone. Another financial panic in 1901, the year before the museum was completed, could have pushed the museum's board to delay the sculptures. No matter the cause, the unfinished limestone has become part of the museum's character and was included in the landmark designation report in 1967.