From a TIME magazine article by Richard Corliss, June 22, 1987:

Dawn Steel, president of production at Paramount, recalls that Mamet's first draft was an "outline, very sparse." How sparse? Capone was hardly in it. To flesh out Mamet's bare-bones script, Steel and her boss Ned Tanen wanted De Palma. "In the past," she says, "Brian hasn't chosen the material that was worthy of him and that he was worthy of. He was making homages to Alfred Hitchcock. This one is a homage to Brian De Palma -- he felt it instead of directing it. With this picture he became a mensch." It surely marked a ! change from the snazzy, derivative thrillers (Carrie, Body Double) and dope operas (Scarface) that made him notorious. The new picture would be neither parody nor eulogy; it would be the story of a straight arrow, told with a straight face.

There are the familiar De Palma touches: lots of photogenic blood, a gorgeous tracking shot that leads our heroes from euphoria to horror, an endlessly elaborate set piece reminiscent of the Odessa Steps sequence in Potemkin. But the director's chief contribution is to the film's handsome physical design. "I wanted corruption to look very sleek," he says. "Some people in positions of power with ill-gotten money insulate themselves with over-the-top magnificence. They buy paintings and expensive clothes. And deep inside they know they're cheats and killers."

Visual Consultant Patrizia Von Brandenstein (Amadeus) accompanied De Palma to Chicago to devise the film's production design. "I thought about these four unlikely little guys going up against the mythic monolith of Capone," she says. "So I used architecture that showed mass and power: the Chicago Theater for the opera house, Louis Sullivan's Auditorium Building for Capone's hotel, a spiffed-up Union Station for the Odessa Steps sequence. Fortunately, Paramount let me really run wild."

I get hung up on this stuff, too, though it’s easy to easy to overlook the lies, narrative or visual, for other compensations. “The Untouchables,” for example. Director Brian De Palma and Chicago-born screenwriter David Mamet filmed a lot of their 1987 Eliot Ness/Al Capone saga here, at Union Station, or on the Michigan Avenue bridge over the Chicago River.

Factually the film is full of it, and I don’t mean facts. It makes stuff up. (It’s a fictional narrative based a little bit on fact; in other words, not a documentary.) At one point, Mamet bailed on rewrites ordered up by producer and fellow Chicago native Art Linson involving Ness tossing gangster Frank Nitti off a rooftop.

It’s a pretty dumb scene, but “The Untouchables” has many I love. Some take glorious advantage of filming here, in the city where the story is set, as in the simple establishing shot of Kevin Costner, Sean Connery, Andy Garcia and Charles Martin Smith crossing LaSalle Street, backed by the 44-story wonder that is the Chicago Board of Trade Building. That famous corridor has never been given grander screen treatment, with the possible exception of “The Dark Knight.”

Chicago as an authentic 20th-century screen entity has a sadly incomplete history, largely thanks to Richard J. Daley. In 1957, NBC-TV premiered the Chicago-set police drama “M Squad,” starring Lee Marvin as the tough guy who, decades later, inspired Frank Drebin in “Police Squad!” and the subsequent “Naked Gun” movies.

Daley and then-Police Commissioner Timothy O’Connor had no love for it. In their eyes, “M Squad” made Chicago look bad. A 1959 epsoide depicted a cop on the take, which made Daley vow never to make special accommodations for outside film crews. That same year, Marvin told TV Guide: “We shoot locations, twice a year. No permit, no cooperation, no nothing. They don’t want any part of us .… Any public building, but nothing else, no stopping traffic. We shoot it and blow.”

A decade later “Medium Cool,” with its culminating scenes filmed during the downtown Chicago melee during the August 1968 Democratic National Convention, gave the city and the mayor another image problem. Daley let John Wayne and “Brannigan” film here, in the mid-’70s, but only when the Jane Byrne mayoral years commenced did Hollywood feel welcome and free to take over Chicago’s streets and beat things up a little, the way the 1980 smash-‘em-up “The Blues Brothers” did.

“Judas and the Black Messiah” may not give you any of the real or period-approximated Chicago of the Fred Hampton years, but Cleveland turned out to be a reasonably effective substitute. Oddly, it’s “The Trial of the Chicago 7″ that looks and feels more fraudulent in terms of atmosphere, even though Sorkin filmed some scenes here.

Moral of the story? You never know. Filming “Holidate” here wouldn’t have saved “Holidate.” And, though I love it, the Chicago-set and Chicago-filmed “Widows” apparently had just enough script issues and knotty storylines to prevent it from connecting with the mainstream audience it deserved.

We’ll close with a little-known story behind the Union Station sequence in “The Untouchables.”

At the time, cultural historian [Tim] Samuelson was working for the Commission on Chicago Landmarks, helping with location scouting for De Palma’s crew. They needed, as he recalled, “a building that looked like a 1920s hosptial with a lot of stairs in front of it, plus a landing.”

Samuelson told them about a couple of churches he knew, here and there. Those might work, he said. How about a church instead of a hospital? No, doesn’t fit the script, the crew said. Well, the only other place, really, is Union Station, Samuelson replied.

A day or two later: “Thanks a lot,” one of the production liaisons told Samuelson, laughing. “Thanks to you, we had to rewrite the whole (expletive) script!” And that’s the scene we have today, filmed on the steps of our beautiful downtown train station, the only possible location for such a preposterously effective homage to the Odessa Steps sequence in Sergei Eisenstein’s “The Battleship Potemkin.”

It never really happened. It’s fiction. But you know? Who cares?

From James Southall's 2013 review of Ennio Morricone's Untouchables soundtrack, via Movie Wave:

De Palma has always believed that music has a very important role to play in a film and as such, the scores for his films tend to be striking and very much at the forefront; and he’s worked with some wonderful composers including Bernard Herrmann, Pino Donaggio, John Williams, Ryuichi Sakamoto, Danny Elfman and others. On three occasions, he worked with the great Ennio Morricone.

The first of those was The Untouchables (with Casualties of War and Mission to Mars to follow in later years) and Morricone’s up-front, arresting music is quite brilliant. The score opens with “The Strength of the Righteous”, which introduces the main action theme (one of five major themes in the score), as electronic beats accompany a repeating five-note phrase heard on low-end piano and then strings, all with a wailing harmonica accompaniment. It’s a portentous opening to film and score – particularly dark yet somehow wonderfully colourful as well. Interestingly, of all the great melodic themes in the score he could choose from, when he performs the music in concert it is this dark action piece that Morricone chooses. The harmonica theme without the five-note accompanying figure is heard in the brilliant-but-brief “In the Elevator”. “The Man with the Matches” is another reprise of the material, this time filled with even more tension (and on the extended version of the album, appended with the brief “Nitti Shoots Malone”, adding a brilliant piece of anguished string writing to the end of the piece). The previously-unreleased “Courthouse Chase” is a brilliant variant on the material, on this album providing a good introduction to the familiar “On the Rooftops”, the score’s primary action cue.