Beginning on the afternoon of Sept. 9, 1968, renowned photographer John G. Zimmerman chronicled the 36 hours that changed tennis. On assignment for Life, Zimmerman went along with Arthur Ashe on his remarkable journey. His photos (below) are being shown for the first time in a new book, Crossing the Line: Arthur Ashe at the 1968 US Open, published by Hannibal in cooperation with the John G. Zimmerman Archive. They capture not just a sport in transition, but a man as well. Ashe would evolve from an athlete who could go unrecognized on the subway to a prominent civil rights advocate before his death in 1993.