On the surface, the scene on Columbia University’s campus appeared to have returned to normal after a spring semester rocked by pro-Palestinian encampments and police crackdowns. Students ate lunch on green lawns last week and tapped a volleyball back and forth under sunny skies.

But, “like a horror film,” said Reinhold Martin, an architectural historian at Columbia, “there’s something wrong with this picture.”

Missing were the children on walks from nearby preschools and the neighborhood residents with their dogs. Also gone were the New York City characters, like a man who used to hang out on the plaza flipping plastic bottles with his feet into a nearby trash can.

Because of a fear that protests could re-escalate, the gates of Columbia’s campus have been closed since the fall semester began, and only people with a Columbia ID can enter. It is a highly unusual situation for an institution that has long taken pride in its openness. Inside the gates, the vibe is tenser and more divided, students and faculty members said.

Rosnel Leyva, a junior, used to bring friends from across the city back to campus to see his “little garden in the midst of Manhattan,” he said, sitting on the library steps. Now, he said, “it’s more like the fall of paradise.”

Elsewhere across the country, students and faculty members said the campus experience has changed at schools that had pro-Palestinian protest activity after the Oct. 7 attacks on Israel and the ensuing war in Gaza. Stricter rules about protests have helped to tamp down demonstrations so far this semester. But underneath the relative calm, students and faculty members say feelings of loss, anger, fear and frustration remain.

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