One black-and-white photograph turns up several times in Thomas Allen Harris’s “Twelve Disciples of Nelson Mandela,” to be shown tonight on PBS’s “P.O.V.” series. It shows a dozen young black men, half of them seated, the other half standing behind them as if for a class picture, most with beaming smiles. As Mr. Harris points out in this important documentary, some called them the Twelve From Bloemfontein, for the South African city where they lived. The photo was taken almost half a century ago, not long before the men piled into two cars and left their homeland, telling their families they were going to an out-of-town soccer game.

They were, in fact, on a global mission: to tell the world about the horrors of South African apartheid, spreading the message of the African National Congress, advocating sanctions and boycotts. It was 1960, just two years before the A.N.C.’s charismatic activist Nelson Mandela was arrested. He remained in prison until 1990.