They move in and out of the building throughout the day. Some appear to work in an informal market out front; vendors sell T-shirts, used books, handmade journals and jewelry, marijuana paraphernalia and food. A sound system outside the auditorium blasts hard-core punk music.

Ambrosio Velasco Gómez, a former director of the School of Philosophy and Literature, adjacent to the auditorium, said that during his eight years running the department, he repeatedly tried to engage the occupiers in a dialogue that might have led to an end to the occupation.

He never got a handle on how many occupiers were maintaining control of the place. On some visits he might have crossed paths with six to eight occupiers, he recalled, adding: “But they have networks of people and in a few minutes there could be 200.”

The group claims to have an open-door policy, though it comes with limits: One occupier said that most everyone but the news media, political party representatives and governmental authorities were welcome.

Occupiers also tried to block a New York Times photographer from taking photos, even of the exterior, claiming that it would compromise their security.

Beyond the lobby and cafeteria, the auditorium itself is now empty; the chairs were long ago removed, leaving only terraces. During a recent visit, the entire place looked tidy and swept.

The occupiers have been accused of dealing drugs and running other criminal operations out of the building, charges they deny. But many in the broader community say the persistence of the occupation has contributed to a culture of lawlessness on the campus.