“Across the River and Into the Trees” presents Liev Schreiber as the latest Ernest Hemingway literary alter ego to make it to the screen, and perhaps the best ever at capturing the world weariness of the late life, post-World War II “Papa” of American literature and legend.

A stately, pristine period piece, it’s a classic “fall film” in its themes, tone and appeal. Beautifully acted and handsomely mounted, it leans into its sadness and its seriousness.

It’s unapologetically a movie for grownups, folks who have read some books, traveled a bit, tasted the wine and lived the opera that life presented to them.

Set a few years after World War II and before the death of “Uncle Joe” Stalin, at the birth of the Cold War, it’s about an old soldier undertaking one last mission — a “duck hunt” in the marshes off Venice, Italy.

But we get the news that Col. Cantwell (Schreiber) has probably suspected for many months, that he’s dying and those nitroglycerin pills he takes for his chest pains won’t be enough. His Army doctor (Danny Huston, perfect as always) barks about the hospital Cantell needs to be in “NOW. Today!”

But not before this drive down to Venice. After that, “I’ll let you prolong my life as much as you’d like.”

Captain O’Neill (Huston) assigns him a driver for his Cadillac convertible, against Cantwell’s wishes. The young sergeant (Josh Hutcherson) isn’t proper “GI” in his decorum around a superior officer. Blame the hero worship. Everybody seems to know Col. Richard Cantwell, who “fought in two World Wars, the “grunt’s” grunt, a real combat soldier. Cantwell can’t wait to ditch the kid.

That fame goes for Venice, as well. Cantwell has a favorite hotel, the Gritti Palace. And everybody, from the Gran Maestro (majordomo, played by Enzo Cilenti) to the barman knows the Col., his favorite drink (martini) and his unusual requirements.

He wants a boat, for duck hunting. H needs duck decoys. And he requires a couple of fowling pieces, shotguns for shooting ducks. Those can be acquired from a widowed contessa (Laura Morante) whose ancient, titled family is a bit short of cash. That negotiation will require more than one visit and a bit of “begging” to help her save face.

Perhaps the fact that Cantwell’s met her beautiful, young and newly-engaged daughter Renata (Matilda de Angelis), will help. She delivered him to the hotel on the family motorboat. Her love of America and indifference to her arranged engagement to a son of wealth means she’ll take an interest in this older man, and he’ll indulge in a paternal flirtation.

But there are still plenty of fascists around and “toy soldier” Italians who don’t like Americans in uniform asking questions. Because Cantwell’s got something other than ducks he’s hunting.

Director Paula Ortiz (“Teresa,” “The Bride”) and veteran British screenwriter Peter Flannery (“The One and Only”) take their time with this tale, immersing us in this life and in this world of luxury and first class travel unblemished by the recent war.

Hemingway fans will relish this taste of how journalists remember Hemingway as a “war correspondent” — looking for action, insisting on the finer things at the end of every day, “combat zone” be damned.

There’s no hint of shortages, no suggestion of Venetian privation greeting the American with his big black Cadillac and love of fine firearms and the perfect martini.

Schreiber gives us a Papa avatar who has seen the wars and fought in them, a man of experience, culture — he stops and makes his sergeant-driver appreciate half-ruined frescoes in an ancient, bombed-out cathedral — and confidence. He’s got little patience for this kid his doctor has assigned as his minder, except as someone to lord over, dismiss or mentor. Cantwell drawls his disappointment at the lad’s lack of push-back at his dismissal.

“For a minute there, I though you had some lead in your pencil.”

Schreiber is magnificent in the part, understated, his beard peppered with white and his eyes giving away the world weariness of a man who has seen much, processed it and is just cynical enough to wonder what it all was for.

War? “It’s a business.”

And mortality?

“I have death sewn into the lining of my clothes.”

Like “Old Man and the Sea” and “Islands in the Stream,” the narrative embraces the Hemingway legend much as the author mixed in his real life in his fiction, identifying with older men as he aged into the relic he most feared becoming.

“Across the River and Into the Trees” is sedate to the point of “slow,” old fashioned to a degree that will feel dated, and yet every minute of it — every gorgeous image, every twist and turn, even the predictable ones — is to be savored.

Rating: unrated, bloody combat, smoking, profanity

Cast: Lieve Schreiber, Matilda de Angelis, Josh Hutcherson, Laura Morante, Enzo Cilenti and Danny Huston

Credits: Directed by Paula Ortiz, scripted by Peter Flannery, based on the novel by Ernest Hemingway. A Level 33 release.

Running time: 1:47