Brutalism, an architectural style which derives its name from the French term béton brut or “raw concrete,” isn’t for everyone. In fact, some people downright hate it. President Trump called D.C.’s Brutalist FBI building “one of the ugliest buildings in the city.” That being said, the movement changed how people thought about and used the material as well as produced a number of important Chicago structures.

“Concrete buildings recall a time when our country invested in the civic realm, when government could be a positive caretaker of its most vulnerable people, when the nation could sincerely express collective aspirations and openness through monumental structures, and when the future could be embraced with optimism,” architecture professor Mark Pasnik said in a Boston Globe op-ed.

Popular during the 1960s and 70s, Brutalism should not be overlooked for its historical importance. Though Chicago lost a few Brutalist buildings—most famously Bertrand Goldberg’s Prentice Women’s Hospital, which was demolished in 2014—the style might even be poised for a comeback.

“In many cases, concrete buildings captured the aspirations of the city at critical times,” Chicago-based architect Iker Gil said in a statement last year. “As we shape the future of Chicago, it is worth trying to learn from the lessons and opportunities represented by these remarkable buildings.”