The granite and marble structure was designed by architect John Duncan, and completed in 1897. The National Park Service maintains that it is the largest mausoleum in North America. Duncan took as his general model the eponymous structure, the tomb of Mausoleums at Halicarnassus, one of the seven wonders of the world; or rather a modern execution of a conception of it, since it is not known what it looked like. A huge public subscription paid for it. Over a million people attended Grant's funeral parade in 1885. It was seven miles (11 km) long and featured Confederate and Union generals riding together in open victories, U.S. President Grover Cleveland, his cabinet, all the Justices of the Supreme Court, and virtually the entire Congress. The parade for the dedication ceremony of the tomb, held April 27, 1897, the 75th anniversary of Grant's birth, was almost as large and was headed by President William McKinley. New York City was chosen as the burial site so that Mrs. Grant could visit frequently, and because Grant was grateful to New Yorkers for their outpouring of affection during his later years.
source: Wikipedia