When “The Lord of the Rings” was first published in the mid-1950s, author J.R.R. Tolkien’s friend and colleague C.S. Lewis wrote, “Here are beauties that pierce like swords or burn like cold iron; here is a book that will break your heart.”

Lewis was referring to the trilogy’s inherent bleakness. Not only did Tolkien create a world from scratch, he gave readers a front-row seat to its dismantling. His Middle-earth was a place of tremendous beauty, but also of gut-wrenching sadness, where characters wandered through the crumbling fortresses of their ancestors, hopelessly dreaming of a return to days long past.

It’s a testament to director Peter Jackson’s brilliance that many of the most memorable set pieces from the film series -- the Mines of Moria, the Elves’ woodland realm, the stronghold of Helm’s Deep and now the marvelous city of Minas Tirith — exist in this context. With “The Return of the King,” Jackson completes the greatest fantasy saga of all time, a film achievement that captures not only the visual splendor of Tolkien’s universe, but the sorrow of everything that takes place within.

Sure, “King” has a happy ending, depending on your definition, but how can saying goodbye to these characters and this world be cause for celebration? It’s not, but we have to move on.

This will be no easy task, since the release of “King,” the trilogy’s money shot, seems to signal something of a turning point in mainstream cinema. It means a big-budget film can no longer be merely the sum of its special effects. It means CGI must forge a peaceful coexistence with story and character development. It means Every Noun should begin with a Capital Letter.

It also means we can expect one of two things: a boatload of great fantasy films or, more likely, a parade of stuff that pales in comparison. Jackson has made George Lucas’ new “Star Wars” movies look like digital “Sesame Street” episodes, and an adaptation of Lewis’ “The Lion, the Witch and the Wardrobe” is in pre-production, but can it possibly be as good as this?

Anyhow, why worry about the future when the present is so exciting? “King” may represent fantasy’s last hurrah, but at least the genre goes out with a bang. It’s the best “Lord of the Rings” movie, delivering a head-rush of visual thrills and emotional poignancy.

Except for a brief expository sequence, the story picks up pretty much where it left off in “The Two Towers.” The members of the fragmented Fellowship of the Ring reconvene at Minas Tirith, the capital of Gondor, to defend the city from attack by Sauron’s forces. The resulting battle easily ranks among the finest action sequences ever filmed. Jackson’s attention to details large and small makes the war, however fantastic, excruciatingly real.

The magnificent epic splatter of the battle sequence is offset nicely by the film’s emotional core, the journey of Frodo (Elijah Wood), Sam (Sean Astin) and the trilogy’s most fascinating creation, Gollum, who is nothing short of a marvel of modern filmmaking. Their relationship evolves into sort of a Freudian three-way psychodrama. Gollum, having lost the battle between his split personalities, turns to evil. His continued struggle against the good-hearted Sam dramatizes the division of Frodo’s deteriorating mind into id (the self-gratifying desire for the “precious” ring) and ego (the need to destroy it).

This storyline leads to the film’s most harrowing scene, an encounter with Shelob, a giant man-eating spider that lives in a Cave guarding the entrance to Mordor. As Gollum leads Frodo into the monster’s clutches, Jackson spins together a sequence that recalls the primal terror of Ridley Scott’s “Alien,” creating a kind of claustrophobic dread few horror directors are capable of producing.

Even during the film’s centerpiece battle sequence, individual character triumphs shine through. Gimli (John Rhys-Davies) and Legolas (Orlando Bloom) mostly are reduced to fringe players, though Legolas gets the most jaw-dropping action scene, and Gimli gets the best one-liner. Merry (Dominic Monaghan) and Pippin (Billy Boyd) get their chance to be heroes. But naturally, Aragorn (Viggo Mortensen) and Gandalf (Ian McKellen) carry most of the heroic weight, thanks to triumphant performances by both actors.

The ferocity of the Pelennor Fields battle makes the siege on Helm’s Deep in “The Two Towers” look like a game of tiddlywinks, and the Nazgul reclaim much of the terrifying power they lost in the second film. The cutting of Christopher Lee’s Saruman (which certainly will be restored on the extended DVD) is the film’s only notable weakness, but when all is said and done it hardly feels like a loss.

I could go on describing the film’s visual treats and terrors, but there isn’t time or space, and there aren’t enough Oscars in the world to appropriately honor Jackson’s accomplishment, or that of the cast and crew.

With the trilogy’s completion, “The Lord of the Rings” has become a singular event in the history of cinema, representing the first time filmmaking on this scale has been executed with such unbelievable success.

I wish it never had to end. “The Lord of the Rings: The Return of the King” is rated PG-13 for intense violence and frightening images. **** out of ****