Today in history: On March 21, 1965, civil rights demonstrators led by the Rev. Martin Luther King Jr. began their third attempt to march from Selma to Montgomery, Alabama — this time under the escort of U.S. Army and National Guard troops assigned by President Lyndon B. Johnson. Also on this date: In 1952, the Moondog Coronation Ball, considered the first rock and roll concert, took place at Cleveland Arena. In 1963, the United States closed Alcatraz Federal Penitentiary; over 1,500 inmates