Mason Temple served as a focal point of civil rights activities in Memphis during the 1950s and 1960s. Mason Temple was built between 1940 and 1945 as the administrative and spiritual center of the Church of God in Christ, the second largest black denomination.

Dr. Martin Luther King Jr.’s famous last speech: “I’ve Been to the Mountaintop was given at the Mason Temple on April 3, 1968. Dr. King was assassinated the next day.

Well, I don’t know what will happen now. We’ve got some difficult days ahead.
But it doesn’t matter with me now. Because I’ve been to the mountaintop.
And I don’t mind. Like anybody, I would like to live a long life. Longevity has its place.
But I’m not concerned about that now. I just want to do God’s will.
And He’s allowed me to go up to the mountain.
And I’ve looked over.
And I’ve seen the promised land. I may not get there with you.
But I want you to know tonight, that we, as a people will get to the promised land. ~ Martin Luther King, Jr.

On April 3, 1968, Mason Temple had scheduled the Southern Christian Leadership Conference’s (SCLC) Rev. Ralph Abernathy, King’s associate, as the evening speaker, but when the 3,000 person crowd demanded to hear King, Abernathy phoned King at his room in the Lorraine Hotel and asked him to address the assembly. Dr. King, Abernathy, Andrew Young and other black leaders had come to Memphis to support 1,300 striking sanitation workers who met regularly at the church.

sources:

http://www.cogic.org/foundersweek/mason-temple/

https://en.wikipedia.org/wiki/Mason_Temple

https://www.nps.gov/nr/travel/civilrights/tn1.htm