THESSALONIKI — A protest march by 1,500 far-left activists in the northern Greek city of Thessaloniki turned violent Saturday towards its end, when some protesters threw firebombs and rocks at riot police, who responded with stun grenades and tear gas.

Police prevented the marchers from reaching their intended destination, the campus of the Aristotle University of Thessaloniki. Thirty people were detained, of whom 27 will face charges, police said.

The march was the culmination of a week of protests over the New Year’s Eve eviction of activists who had occupied a room at the university’s biology department for 34 years.

The occupation did not disturb the department’s functioning and the room had become an activity hub. The department decided it needed the room to expand its library and police broke through a locked door into the room, which was empty at the time.

Activists re-occupied the room on Jan. 10 but were evicted in a new police operation the following day. Fifteen people were arrested and their trial has been scheduled for Friday.