6 & 7. Morton F. Plant House and George W. Vanderbilt House, 4 E. 52nd Street, 645 and 647 Fifth Avenue

When John Jacob Astor began to build the St. Regis Hotel on Fifth Avenue in 1901, the wealthy residents in the area started to buy up land to prevent future commercial development. On the corner of 52nd Street and Fifth Avenue, Morgan Freeman Plant, son of the railroad tycoon Henry B. Plant, commissioned architect C.P.H. Gilbert to build him a large stone mansion. The mansion was later allegedly traded to Cartier in a legendarily bad deal that involves a string of pearls Mrs. Plant was particularly smitten with.

George W. Vanderbilt snapped up the land next door and built his “Marble Twins.” Designed by designed by Hunt & Hunt and completed in 1905, the homes, along with Plant’s mansion, were described by the AIA Guide to New York City as “free interpretation[s] of sixteenth- and seventeenth-century palazzi.” The Vanderbilt mansion at 645 was demolished but 647 remains.