This is the big one, a huge, darkly philosophic poem wrapped in a rousing melodrama of lust, cruelty, revenge and expiation, given a very moving, always clear and sometimes thrilling production by Pittsburgh Irish & Classical Theatre.

"King Lear" begins like a fairy tale, saying, "Once there was an old king who split his kingdom between two daughters and disinherited the third one he loved." Why? That's just given. Shakespeare doesn't plumb it further. But he dramatizes what follows to ravage the heart with Lear's laceratingly wise insanity.

James J. Christy stages this great tragedy on a primal disc of dirt, floating in air like the world, backed by two rear walls rich with fiery rust or mottled blue, suggesting a sacrificial altar or Iron Age Stonehenge. Just off center is a tall metal throne, angular in Giocometti torment. To the left is a drum set, and on either side, ladders topped by spotlights.

Into this frankly theatrical arena parades a Lear who has it all figured out: He's going to give his two older daughters and their ducal spouses adequate shares of the kingdom, but he has a queenly share for his youngest, Cordelia, who as her name suggests is closest to his heart. But she, as stubborn as he, won't go along with his planned ritual, and he erupts in mindless vengeance.

His story is paralleled by that of the Duke of Gloucester, two foolish old men, fearful of mortality and misjudging their children, who pay a huge price.

David Gordon's set is a concentrated circle on which to focus a universe of action. It's also a world of performance, set off from ours. As the mid-play storm descends on wandering Lear, the dirt turns to mud, through which the actors struggle as the play turns to grim war. At the circle's edge crouch ensemble members who hand in props as needed. They also toss cups of blood on cue, an emblematic practice familiar in some theater styles that here tests the audience, some of whom found it funny.

The text, pared by about 30 percent by Christy and the star, Dakin Matthews, resonates so fine and clear that I think even a novice could follow most of it with ease. Cuts make lots of choices, of course, beyond the scope of this review.

But this production clarifies many points, as well. It provides Lear with a crown for Cordelia, not just a ducal coronet, clear indication of his hidden plan. He winks to Kent as he sets his daughters to do their party pieces. This is no incipient madman, but a king trying to do the impossible, to control the future.

A live drummer provides processional pomp, augmenting three huge handing thunder sheets rattled in full view as though by heavenly tormentors. Meanwhile, the spotlights provide emphasis or even bright glamour for soliloquies -- they seem especially fond of the bastard (in both senses) Edmund.

In the story, Lear splits his kingdom between his two elder daughters, then lives to regret it every way. The Earl of Gloucester similarly misjudges his two sons. Madness strikes Lear and Gloucester is blinded and left for dead. They find their way to a hovel in a storm and then to the beach at Dover, as Cordelia comes to save Lear and the kingdom goes to war around them. Disaster and transcendence ensue.

There's more incidental humor than you might expect, even in the abridged central hovel scene, as Lear rages madly through his imaginary trial of his daughters. We seem to have reached absolute bottom, but as the play reminds us, there is always a further fall. That comes with Gloucester's horrific blinding.

Christy and his designers engineer Pieta-like images of archetypal pathos, as in the blinded Gloucester, in the arms of his near-naked son disguised as a madman, or in the dying Lear with his dead Cordelia in his arms, hopeful she still lives.

In other hands, the Gloucester story would be a play of its own, but Shakespeare heaps up its agony to parallel and intensify Lear's own. And this subplot provides a climactic battle between Edmund and his legitimate elder brother, Edgar, one corrupted by envy and power, the other purified by suffering.

Only in the final third of the play do we discover the true corruption of the two older sisters, who earlier may seem more sinned against by Lear's intemperance than sinning. This redresses the balance and allows us our full tragic sympathy for Lear.

Pei-Chi Su's costumes are spare like the set: it's the words that convey nobility. Lights and sound join the set to make spareness noble.

Although Christy sets the play in no particular age, it feels early medieval. So I question such glaring anachronisms as when Gloucester enters the storm scene not with a lantern but a large and jarring flashlight. At least that prepares us for the interrogation light that descends for the grilling that leads to his blinding.

PICT has pulled out all the stops to enlist as good a cast as Pittsburgh offers, strengthened by notable imports led by Matthews, who plays Lear and also god, serving as dramaturg and cutting the text in conjunction with Christy.

No actor can play every facet of this epic king. In Matthews, I miss the irascible tyrant who could build a kingdom. I don't see the iron. But Matthews is wonderful on other counts. Our sense of his trembling sanity is acute (you can see he really fears a stroke), and he does reach for extra vitriol as he curses his rapacious older daughters with a violence that must have long festered in his heart.

Matthews is most moving when he sinks from rant into musing ("that way madness lies") and querulous confusion. He can get laughs -- "Didst thou give all to thy daughters?" got a big one from Sunday's mainly older matinee crowd. He's never better than in his mad scene at Dover, where he who once ruled discovers with lacerating insight that even "a dog's obeyed in office."

On his "foolish, fond old man" confession, my eyes misted just as he asked, "be your tears wet?" And Matthews has the questing intelligence and sweet sorrow which, confronted by his own folly in the presence of the martyred Gloucester and Cordelia, made my eyes stream.

Bradbury's Fool is a gnarled, bent creature, cowering, scampering, playing the gadfly one minute and the whimpering child the next, issuing gnomic pronouncements with a mixture of glee and dread. He is clearly an agent of Lear's gradual revelation and thus disappears from the play when his work is done.

You need a second Lear to play Gloucester, and PICT has one in Larry John Meyers, rich in pathos. As his older son, David Whalen's Edgar takes the agonizing journey through the mud to self-realization. Interestingly, Matthews' cutting reintroduces the old question about whether Edgar actually goes mad while pretending to be -- either way works. As Gloucester's bastard, Edmund, Paul Todaro is a supremely self-confident villain with the snotty shine of glib charisma.

The two older daughters, Helena Ruoti's Goneril and Robin Walsh's Reagan, are as complex as their great skills and Shakespeare's too few lines allow. Neither is a fool, and their eventual competition for Edmund's favors could make a play by itself.

There are other performances to enjoy: Matt DeCaro's solid Kent, Dereck Walton's creepy Oswald, Karen Baum's saintly Cordelia, Randy Kovitz's upright Albany and Mark Staley's rapacious Cornwall.

I guess the only serious objection would be that levied long ago by Samuel Johnson: It's just too painful to enjoy. But seeing "Lear" played this well, it fills the mind and heart.