On April 16, 1963, Dr. Martin Luther King Jr. sat in a Birmingham, Ala., jail, penning words that would stir the nation’s conscience and resonate with meaning for years to come.

King was arrested for violating a court injunction against mass public demonstrations in the southern city which had become a nucleus of the civil rights movement.

Fifty years later, Dr. King’s daughter joined more than 100 people outside the former jail to unveil a marker in honor of her father’s famous “Letter from Birmingham Jail.” Others all over the world gathered to commemorate the 50th anniversary of the important civil rights document, which has been translated into 40 languages and which contained the oft-quoted line “injustice anywhere is a threat to justice everywhere.”

“The City of Birmingham tried to run him out of town and now is honoring him as one of their heroes. How times have changed,” said Bernice King, the civil rights leader’s youngest daughter and chief executive officer of the King Center in Atlanta, according to Reuters.

King joined Gov. Robert Bentley and other officials to dedicate the new marker outside the former jail, now an administrative office for the Birmingham Police Department. The original jail cell is on display at the Birmingham Civil Rights Institute.

Ensconced in that cell, King wrote the letter on scraps of paper, responding to eight White clergymen who criticized his anti-segregation demonstrations as “unwise and untimely.”

“You deplore the demonstrations taking place in Birmingham. But your statement, I am sorry to say, fails to express a similar concern for the conditions that brought about the demonstrations,” King said. He added, “It is unfortunate that demonstrations are taking place in Birmingham, but it is even more unfortunate that the city’s White power structure left the Negro community with no alternative.”

Going past those eight ministers, King’s letter grew into an overarching chastisement of White moderates, whom King called “the Negro’s great stumbling block.” Those moderates said they supported the civil rights movement’s cause but not its methods and often urged patience.

“For years now I have heard the word ‘Wait!’ It rings in the ear of every Negro with piercing familiarity. This ‘Wait’ has almost always meant ‘Never,’” King wrote. “ we must come to see, with one of our distinguished jurists, that ‘’ ‘justice too long delayed is justice denied.’”

Clayborne Carson, director of the Martin Luther King Jr. Research and Education Institute at Stanford University, told The Birmingham News that King’s letter grew into a manifesto.

“King initially intended the Birmingham letter as a response to the eight clergymen, but it became the most cogent and influential defense of nonviolent resistance ever written,” he said.

Beyond that, experts say, the letter has global appeal because it exudes King’s love and concern not only for his own people but for humanity.

“He speaks to all oppressed people, and that’s his basic Christian concern,” Jonathan Rieder, a professor at Barnard College and Columbia University and author of “Gospel of Freedom: Martin Luther King’s Letter from Birmingham Jail and the Struggle That Changed a Nation,” told The News. “That’s why he’s upset about the appalling silence of the good people.”

Even in his righteous anger, however, King expresses hope, concluding his letter with the expressed wish to meet with his fellow clergymen and to see an end to the divisiveness that plagued the nation.

“Let us all hope that the dark clouds of racial prejudice will soon pass away and the deep fog of misunderstanding will be lifted from our fear drenched communities, and in some not too distant tomorrow the radiant stars of love and brotherhood will shine over our great nation with all their scintillating beauty,” he wrote.