Steve Buscemi plays the part of Nucky Thompson in a scene from HBO’s “Boardwalk Empire,” premiering Sept. 19.

On a blistering afternoon last June, outside a Polish social club in Greenpoint, men in heavy wool tuxedos, with slicked-back hair and pencil-thin mustaches, were blotting their brows. They looked like overheated figures from a Peter Arno drawing. Nearby were some very slender young women in spangly, ankle-length dresses. A couple were wearing feathered headdresses; others had their hair in paper curlers. But because this was Brooklyn, where people wear weird getups all the time, nobody paid them any attention.

A few blocks away, on a lot once intended for a condo complex, a 300-foot-long old-fashioned seaside boardwalk had miraculously arisen, not just a facade, but a collection of clubs, restaurants, a photo studio, salt-water taffy joints, even a place where for 25 cents you could have peered at premature babies. Except that the incubators were empty. So were the shops.

This brand-new ghost town is the $5 million set for “Boardwalk Empire,” a new HBO series that begins Sept. 19. For more than a year now it has periodically sprung to life with hundreds of actors, like the ones milling outside the social club. They were getting ready to film a supper-club scene in which Hardeen, Houdini’s younger brother, escapes from an upside-down straitjacket.

“Boardwalk Empire” is set in Atlantic City in 1920, during the first year of Prohibition, and the big outdoor set, the vintage clothing and the kind of historical research that delights in Houdini’s sibling are all evidence of the unusual, painstaking lengths the show’s creators have gone to re-create an era that barely registers in the American historical consciousness.

The series “Boardwalk Empire” is based in part on a book by the same name, a history of Atlantic City from its creation in the 19th century up to the present, by Nelson Johnson. In 2006, HBO, already looking for a big series to replace “The Sopranos,” showed the book to Terence Winter, who wrote many “Sopranos” episodes. “They said, ‘maybe you’ll find something here,’” Winter recalled, “and they added that, ‘oh, by the way, Martin Scorsese is attached to this if it goes anywhere.’ I said that in that case I would absolutely find something.” Scorsese wound up directing the pilot episode and became an executive producer of the series.

Winter was interested in the ’20s, and in Enoch Johnson, known as Nucky, by far the most vivid character in the book. The appeal of the period was that it had seldom been done on TV or even in the movies, he said.

Nucky Johnson (no relation to the author of “Boardwalk Empire”) was a political boss and stalwart of the Republican Party who from 1911 to 1941 controlled all the vice in Atlantic City.

The real Nucky was tall and broad-shouldered, with an enormous, domelike head. In the show, fictionalized slightly as Nucky Thompson, he’s played by the bug-eyed, slightly cadaverous Steve Buscemi, another “Sopranos” alumnus. “If we wanted the real Nucky, we would have cast Jimmy Gandolfini,” Winter said, “but by Episode 12, you’re going to think nobody else could have done it but Steve.”

Winter said he and Scorsese refused to fudge some of the historical detail, even though by doing so they could have saved a bundle and no one would have noticed. “If you’re going to this kind of thing, the little details are what’s important,” Winter said.

The big details are important, too. Prohibition didn’t just give rise to a generation of Charleston-dancing, flask-waving tipplers. It unloosed a wave of greed and violence. Atlantic City welcomed the 18th Amendment, seeing in it a huge financial windfall, and the characters in the show, authentic and imaginary, are besotted with money as much as with booze.

“We have whiskey, wine, women, song and slot machines,” the real Nucky once said. “I won’t deny it, and I won’t apologize for it. If the majority of the people didn’t want them, they wouldn’t be profitable.”

‘Boardwalk Empire’

When: Sept. 19

Where: HBO