If you walked across the campus of Columbia University in April 1968, you may have been handed a typewritten flyer inviting you to a campus protest. “The big steal is on,” it declared. Columbia was in the process of stealing land and resources from nearby Harlem, the flyer claimed—and students could help stop it.

The students who passed out those flyers may not have realized it, but soon they’d be part of a controversial occupation of Columbia University that would spark one of the largest mass arrests in New York City history. By the end of the uprising, five university buildings would be taken over by nearly 1,000 protesters and the campus would be on lockdown after its dean was taken hostage.

And the gym that partially sparked the protest, which was mockingly called “Gym Crow” by its detractors, would become a symbol not only of the unrest, but of an epic struggle between a historic university and the broader community.

Columbia is located in Morningside Heights on the edge of West Harlem, and in 1968, a plan to include the community in a proposed gym building exploded in the university’s face. The monumental concrete gym was to be built in Morningside Park, which is owned by New York City, and though it was built on public land, only 12 percent of the gym would be open to the public. The other 88 percent would be set aside for Columbia’s use.

This plan wasn’t welcomed by the community, especially in light of Columbia’s years-long expansion into Morningside Heights at the expense of residents—most of them African-American—who were evicted and pushed out of their homes. Harlem residents resented Columbia taking over precious recreation space and making a half-hearted gesture to include the community even though the project was moving forward against their objections.

One facet of the gym in particular—a community entrance at the bottom of the building while Columbia students entered from the top—drew particular ire.

“It’s the symbol of coming in through the back door that bothers the black people,” a Columbia professor explained to LIFE Magazine. “That’s why they call it the g-y-m crow door.”

“People saw it as Ivy imperialism,” says Stefan Bradley, associate professor and chair of African American Studies at Loyola Marymount University. “The gymnasium was just so concrete.” Bradley’s book, Harlem vs. Columbia University, tracks the complicated, chaotic story of what happened next.

Black Columbia students in the Student Afro-American Society (SAS) felt responsible for representing the complaints of African-Americans in Harlem, and they brought their concerns to a campus that was already in foment. As the Vietnam War ramped up, student activism had reached a frenzied peak on campus, and members of Students for a Democratic Society (SDS), an anti-war group, were escalating calls for Columbia to stop associating itself with the Institute for Defense Analyses, IDA, a research group that worked with the Department of Defense.

“The two strands of anger and disgust converged,” SDS member Nancy Biberman told Vanity Fair: “what the university was doing to aid the war effort, and what the university was doing that was racist in our neighborhood.”

As those forces intertwined, so did students—for a while. On April 23, 1968, protesters gathered in the center of campus for a rally. Then, students rushed into Hamilton Hall, home to Columbia’s administrative offices and some classrooms. As administrators begged them not to take their protest indoors, the students moved in.

Word of the occupation spread across campus and into Harlem, but inside Hamilton Hall, tension was building between the black SAS students and the majority-white SDS. The SDS wanted to take an administrator hostage and use the occupation to draw attention to their anti-war work, but the SAS wanted to stick to their issue of stopping construction at the gym. Finally, the black students asked white students to leave the building.

Though the move was painted by white commentators as an expression of black militancy, Bradley says it was a strategic choice on the part of the African-American protesters. “The black students knew that it would be difficult for the university to approach a black-occupied building, especially in light of all of the uprisings in Harlem,” he said. By confining their gym-related protest to a single building, black students could represent the community’s opposition to the gym while other students broadened the occupation to reflect their opposition to the war and other issues.

Hamilton Hall was soon transformed into living quarters for the 86 black protesters, who covered its walls with portraits of Black Power leaders and renamed it the “Malcolm X Liberation College.” They set up a food pantry, slept on the floor, and welcomed black visitors. Meanwhile, the university struggled to figure out how to kick them out. If they used force, they feared, a riot might break out not just at the school, but in Harlem. Given the national racial tensions that had been heightened by the assassination of Martin Luther King, Jr. just weeks earlier, it was a tenuous time.

The occupation lasted a week, with students rebuffing administrators’ attempts to strike a deal. Then, at 2:00 a.m. on April 30, nearly 1,000 police gathered on Columbia’s campus.

Their first destination was Hamilton Hall, where all 86 students surrendered without a fight. “They knew what police could do,” says Bradley. “It wasn’t just a story or tale or lore—they would kill young black people if necessary.” Meanwhile, police met resistance from white protesters. They made over 700 arrests and injured over 100 students, clearing out the buildings as protesters stampeded.

Ultimately, the occupation gave students at Columbia more power, resulting in the creation of campus structures designed to give students a voice and a vote in university matters. Black students eventually were able to convince the university to add more black faculty members, admit more black students and create a Black Studies program. And in March 1969, the university dropped plans for the gym.

“A minority of a minority was able to change a white institution that had been around before the United States had been established,” says Bradley. “I think this is remarkable.”

Bradley sees parallels between the activism of 1968 and that of today’s Black Lives Matter movement. He notes the same audacity in both movements—and many of the same tactics—in their “ability to take the small things like a gymnasium or these very local matters like the death of Trayvon Martin or Philando Castile or Sandra Bland—these very local things—and turn them into an indictment on systems,” he says. “Students back in the ‘60s and young people today who have taken to the streets have that unique ability to tie the local matters to larger systems.”

The 1968 protests—and the memory of Gym Crow—may be long gone, but their legacy is anything but dead.

WATCH: Why Did Columbia University Students Protest in 1968?