 They decided to build a country house on the east bank, and by a decade later had assembled a property of nearly , about 3 square miles.The resulting estate was named for one of its landmarks, "Indian Council Rock," a cliff overlooking the creek, that was reputed to have been a meeting place for the Lenni Lenape tribe.The 60-room main house was designed by architect Charles Willing in 1928, and built, 1930–1931.