In the late 19th century, the very rich of New York began building mansions along the stretch of Fifth Avenue between 59th Street and 96th Street, looking onto Central Park. By the early 20th century, this portion of Fifth Avenue had been nicknamed "Millionaire's Row", with mansions such as the Mrs. William B. Astor House and William A. Clark House. Entries to Central Park along this stretch include Inventor's Gate at 72nd Street, which gave access to the park's carriage drives, and Engineers' Gate at 90th Street, used by equestrians.