In the mid-20th century, Boston was in a financial and cultural rut — and needed a jolt. Flush with $40 million in federal funds, the city cleared some 1,000-plus buildings — obliterating a historic but increasingly seedy and squalid neighborhood known as Scollay Square — to make way for a new government center. Its centerpiece was a dramatic new City Hall. It was a bold, ambitious statement by a city aiming to turn a corner.

While it was not without controversy or detractors, the building was nevertheless hailed as a grand architectural achievement. In a late 1960s episode of WGBH-TV's "Michael Ambrosino's Show," host Michael Ambrosino walked the area, presenting an up close look at Boston’s new modernist structure and the sweeping plaza surrounding it.

"Boston gambled, and they won," Ambrosino said. "The plaza not only presents City Hall, but it extends right into it. City Hall is the backdrop and we’ve gotta look closely at it to sense the mood it creates on the plaza."

I recently spent a chilly, sunny November morning asking passersby to describe the mood they felt the building created on the plaza in 2018.

"Mildly oppressive," said Becky Cumberland.

"Sad," said Ernesto Martello, who has lived in Boston for 34 years. "That building is not beautiful. How do they build that in a beautiful city like Boston?"

Visiting New Yorkers Nicole Friedlander and Brittany Haiduk both said that it looks "like a jail."

Boston's Thomas Cannon called it "ugly as hell."

Opinions like these were not hard to come by. In 2013, California Home + Design magazine placed our City Hall on its list of "25 Buildings to Demolish Right Now." In 2008, a website, VirtualTourist, named it the ugliest building in the world, an ignominious label that went viral and can still be heard mentioned on Duck Boat tours.

And yet…

"It will go down in history as one of the exemplar works of the 20th century," said Chris Grimley, architect and co-author of "Heroic: Concrete Architecture and the New Boston." Grimley and a few colleagues also created "Brutalist Boston Map: Guide to Brutalist Architecture in Boston" for those interested in surveying the city's numerous concrete buildings. This includes City Hall, built in the mid-20th century architectural style known as brutalism.

"The quick definition of brutalism is — well, there is no quick definition," said Grimley. "But if you wanted to pigeonhole it, it’s a building built out of concrete that’s very expressive in its design."

The word "brutalism" comes from the French, "béton brut" — simply a term for exposed concrete. The brutalist movement was a reaction to the rise of steel and glass. Buildings were designed to be more honest, expressive and heroic — revealing on the outside both the function and energy within. Grimley said City Hall hits all the marks in spades.

"You look at it and you don’t know what to make of it, and it gets you to pause and think about what it’s doing or how it was made," he said. "And I think as you approach it, what initially appears as a monolithic thing starts to become a very transparent structure. And it goes against the idea of this monument of concrete."

As for all the criticism, Grimley lobbies for the long view. He said we’ve always been too quick to judge the aesthetic value of buildings — and too quick to tear them down. He said that in the 1950s, the word "monstrosity" was regularly used to describe Victorian buildings (think those beautiful, tall, red-brick row homes all over Boston's South End). Just like what happened with Victorian architecture, he said the perception of brutalism is finally starting to change. And Grimley’s is not just a local “hot take."

"It’s just so absolutely immense and heroic," said Felix Torkar, a Berlin, Germany-based architecture historian and a member of a group called #SOSBRUTALISM, dedicated to the study and preservation of brutalist architecture around the world. "Boston City Hall is something like the Taj Mahal of brutalism."

Torkar said that City Hall might be the single most influential building of the entire movement.

"Boston City Hall in particular established a whole new building archetype," he said. In fact, buildings modeled on it — or close replicas of it — increased throughout the 1960s and 70s, from a library in Australia to a public swimming hall in Norway.

"There’s a bank in the Dominican Republic, a philharmonic hall in Kyrgyzstan, Israel’s parliament building," said Torkar. "You really see those Boston City Hall clones in the next decade all over the word. And you can really only understand those looking at the original in Boston."

As for that original, Grimley and his firm are now working with the city of Boston to produce a report on the state of the building on its golden anniversary. The idea is to examine what might be undertaken to conserve and renew it so that the building is still standing strong enough to be reevaluated again in another 50 years.

Correction: An earlier version of this story stated Michael Ambrosino discussed Boston City Hall Plaza in a television special. It was in fact an episode of “Michael Ambrosino's Show.” That change is reflected.