Very few non-violent civil disobedience tactics of the late 1950s and early 1960s were as brilliantly simple in conception and as effective in execution as the sit-ins that rocked cities and towns from Texas and Oklahoma to Virginia, Tennessee, North Carolina and beyond. Some sit-ins — at lunch counters, state houses and other public and private venues — were more confrontational than others; some lasted longer than others; some were more high-profile than others. But all of them required a certain kind of courage (Hemingway's phrase, "grace under pressure," comes readily to mind in this context) and a communal willingness to sacrifice that were hallmarks of the Civil Rights Movement in America from the very first.
Here, LIFE.com presents a gallery of photos — many of which never ran in LIFE magazine — from a series of protests and sit-ins in Petersburg, Virgina, in May 1960, and from a broader-themed planning conference sponsored by Martin Luther King Jr. and the Southern Christian leadership Council at Atlanta University earlier that month. The pictures, by LIFE's Howard Sochurek — a Princeton grad, Neiman Fellow at Harvard and WWII Army vet — capture one small but significant exemplar of the sit-in phenomenon, as well as some of the unusual training methods that potential sitters-in endured before taking to the streets and to the seats.
In notes sent to LIFE's editors in New York from the magazine's Washington, DC, bureau in May 1960, the sit-in movement's activities in Virginia were dubbed the "Second Siege of Petersburg" — a tongue-in-cheek reference to the famous siege of the town and nearby Richmond between June 1864 and April 1865 during the Civil War.
The "siege" metaphor, meanwhile, takes on a peculiar resonance in those notes — for example, in a quote from a newspaper publisher in Petersburg, George Lewis, who told LIFE: "I'm against integration. The mood of Petersburg definitely is for segregation. The Negroes are pushing too hard and the whole pace is too fast. Petersburg is not ready for integrated lunch counters. If they integrate them, the whites will boycott. But things are changing slowly. Ten years ago we couldn't have printed a Negro picture in the paper. The whites wouldn't have stood for it. Now we print them when they're in the news. It's a mark of the progress here. But the Negroes are pushing too hard. They've created an explosive situation here in Petersburg."
Describing a key element of that "explosive situation" — the sit-ins by activists at various lunch counters in town — LIFE wrote in its September 19, 1960, issue (published a full four months after the events described):
The key to the sit-in is non-violence, but it takes a tough inner fiber neither to flinch nor retaliate when, occasionally, hooligans pick on the sitters-in to discourage them or provoke them into some violent act. Fearing the stress on sensibilities and temper to which a sit-in could be subjected, the high school and college students of Petersburg, Va. studied at a unique but punishing extracurricular school before they attempted sitting-in.
In the course, which they ironically call "social drama," student are subjected to a full repertory of humiliation and minor abuse. These include smoke-blowing, hair-pulling, chair-jostling, coffee-spilling, hitting with wadded newspaper, along with such epithets as "dirty nigger" and "black bitch." Anyone who gets mad flunks. So far in Petersburg effective police action and the calm attitude of the townspeople have averted trouble.
Except for a few adult leaders ... the sitters-in are youngsters like Virginius Bray Thornton ... In a real sense they are the South's "new" Negro. They are educated, filled with a fierce idealism, chafing impatience and bitterness against the remaining shackles. "This is not a student struggle, it is a Negro struggle," says Virginius. A baffled white man echoes him: "The older Negroes don't want integration but these kids are shaming them into it."