Harbor Hill, a 348-foot rise on Long Island spanning East Hills and Roslyn, is Nassau County’s highest point and was long noted in debates over Long Island’s highest elevation. It became famous as the site of Harbor Hill, Clarence Hungerford Mackay’s immense country house, built from 1899 to 1902 and designed by McKim, Mead and White with strong French inspiration and extensive formal grounds. One of the North Shore’s great Gilded Age estates, it hosted major social events before decline set in; the mansion was vandalized during World War II and demolished in 1947. The hill remains important both geographically and as the surviving setting of a remarkable estate.