To do so, Caro began work on a biography of Moses, "The Power Broker: Robert Moses and the Fall of New York", also a study of Caro's favorite theme: the acquisition and use of power. He expected it would take nine months to complete, but instead it took him until 1974. The work was based on extensive research and 522 interviews, including seven interviews with Moses himself, several with Michael Madigan (who worked for Moses for 35 years); and numerous interviews with Sidney Shapiro (Moses's general manager for forty years); as well as interviews with men who worked for and knew Moses's mentor, New York Governor Al Smith. During the 1967–1968 academic year, Caro worked on the book as a Carnegie Fellow at the Columbia University Graduate School of Journalism.