The images of that day in 1965 were quickly seared into the American consciousness: helmeted Alabama state troopers and mounted sheriff's possemen beating peaceful civil rights marchers in Selma, Ala., as clouds of tear gas wafted around the Edmund Pettus Bridge.

On March 7, 1965 — a day that would become known as "Bloody Sunday" — 600 marchers heading east out of Selma topped the graceful, arched span over the Alabama River, only to see a phalanx of state and local lawmen blocking their way on U.S. Highway 80.

The police stopped the marchers, led by Hosea Williams of the Southern Christian Leadership Conference and John Lewis, chairman of the Student Nonviolent Coordinating Committee, and ordered them to disperse. Then they attacked. Lewis, one of 58 people injured, suffered a skull fracture. Amelia Boynton Robinson, then 53, was beaten unconscious and left for dead, her face doused with tear gas.