Police arrested dozens of Columbia University students who seized part of the school’s main library on Wednesday in one of the biggest pro-Palestinian demonstrations on campus since last year’s wave of protests against Israel’s war on Gaza, Reuters reports.

At least 40 to 50 students, their hands cuffed with plastic zip-ties, were seen being loaded into New York Police Department vans and buses outside Butler Library as NYPD officers swept through the six-story building to round up other protesters who refused to leave.

Police arrived on campus in force at the request of Columbia officials who said the student demonstrators occupying the library’s second-floor main reading room were engaged in trespassing.

Videos and photographs on social media showed protesters, most wearing masks, standing on tables, beating drums and unfurling banners saying “Strike For Gaza” and “Liberated Zone” beneath the chandeliers of the Lawrence A. Wein Reading Room.