Columbia cancelled in-person classes, dozens of anti-Israel protesters were arrested at New York University and Yale, and the gates to Harvard Yard were closed to the public Monday as some of the most prestigious U.S. universities sought to defuse campus tensions over Israel’s war with Hamas.

More than 100 pro-Palestinian demonstrators who had camped out on Columbia’s green were arrested last week, and similar encampments have sprouted up at universities around the country as schools struggle with where to draw the line between allowing free expression while maintaining safe and inclusive campuses.