Purgatory : After years of neglect, some Protestants now believe it exists; many Catholics don’t. For others, it’s not a place--it’s a state of mind.

For centuries, a mysterious Irish island the size of a football field was believed to be a literal gateway to the afterlife. Perfectly healthy visitors were stretched out like corpses, blessed with ritual prayers for the dead and then locked overnight in a cave.

There, they reported unearthly visions, dreams and sometimes actual trips to a realm of torments and delights. In this other world, sinners were seen being devoured by serpents or pierced with flaming nails; demons and animals were heard shrieking in the darkness, and saints walked through jeweled gates to behold skies like molten gold.

Tales of the journeys turn up in numerous diaries and letters from the Middle Ages. And the island, which still lures thousands of pilgrims each year, helped popularize one of the most controversial ideas in Christian history: Purgatory.

For half a millennium, followers of Jesus have argued, excommunicated and occasionally killed each other--at least in part--over the concept of an intermediate state between Heaven and Hell.

First Eastern Orthodox, then Protestants rejected the doctrine.

Lately, even a lot of Catholics seem skeptical. Since the Second Vatican Council 30 years ago, the subject rarely gets mentioned in books or sermons. And a survey by U.S. Catholic magazine found nearly one in four readers rejected its existence.

But Purgatory is hardly in limbo.

Italy has a museum devoted to it. A defense attorney tried to blame Purgatory for an attempted murder. And it has been racking up cameos in literature and film.

Meanwhile, Catholic thinkers have drafted intriguing new blueprints for the hereafter. As a result, support for the idea of Purgatory has emerged from the unlikeliest of sources: theology professors at several conservative evangelical colleges, traditionally among the fiercest opponents of Catholicism.

Nevertheless, Purgatory suffers PR problems. Unlike its more famous cousins, Heaven and Hell, it no longer draws visitors during near-death experiences.

It also is widely misunderstood. Even a few Catholics mistakenly believe that Purgatory offers unsaved souls a “second chance” to qualify for Heaven. Actually, everyone there already has been deemed worthy of Paradise, says Peter Kreeft, a Boston College philosophy professor who writes about the afterlife.

Purgatory is merely a celestial boot camp for incoming saints, where life reviews take place and the last vestiges of self-love and other imperfections are “surgically removed.” Prayers from the living are said to aid the process.

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If Christianity hadn’t invented Purgatory, someone else surely would have. From Dante to “St. Elsewhere,” it has proved to be one of the world’s handiest literary devices.

In 1991, comic Albert Brooks transformed the idea of an afterlife layover into the movie “Defending Your Life.” And “Saturday Night Live” did a spoof of near-death visions in which people returning from Flat-EKG Land recalled going through a dark tunnel to a bright light, where they were told to “take a number” and wait.

Purgatory also appears in Anne Rice’s latest vampire novel and countless newspaper stories.

Even the judicial system has grappled with the concept. In 1982, the lawyer for a former mental patient who stabbed actress Theresa Saldana said his client was driven by a desire to be executed in order to free from Purgatory the soul of an Alcatraz inmate who died in a prison riot.

But Purgatory’s mini-revival in the secular world contrasts with its decline among Roman Catholics. Once a fixture of church subculture--schoolchildren prayed for the souls there and “good death societies” tried to avoid its penalties--the place has lost its allure.

Vatican II knocked the wind out of it, says religion historian Colleen McDannell of the University of Utah. By refocusing Catholic devotional life onto Christ and the sacraments, the council undermined all “peripheral” beliefs.

“Once the [rituals get] devalued, you don’t have any way of reinforcing the theological concept,” she adds. “Purgatory might still exist, but who cares?”

Oddly enough, the answer to that may be . . . Protestants.

One of the first to broach the subject in modern times was author C.S. Lewis. “Our souls demand Purgatory, don’t they?” he wrote. Even if God doesn’t mind people entering Heaven dripping with “mud and slime . . . should we not reply . . . ‘I’d rather be cleansed first.’ [Even if] it may hurt. “

More recently, evangelicals have warmed to Kreeft’s speculations on the next world. A onetime Protestant who converted to Catholicism, Kreeft places Purgatory inside Heaven and says, echoing St. Catherine of Genoa, that any pain felt there is “incomparably more desirable than the most ecstatic pleasures on earth.”

That portrait isn’t much different from what some leading evangelical scholars call the “intermediate state” between death and Paradise, says Gary R. Habermas, a philosophy professor at Jerry Falwell’s Liberty University.

Habermas concedes that the name Purgatory still sets off alarms in most Protestant minds, but says that might change if believers read Kreeft’s ideas. “If the word offends you, call it ‘Heaven’s kindergarten.’ ”

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The origin of Purgatory isn’t easy to pin down. The concept took shape over hundreds of years, in a process that involved everything from disputed Bible passages to reports of ghosts marching through the forests of Europe.

The starting point, says historian Alan Bernstein of the University of Arizona, was the practice of praying for the dead. The custom began in Judaism shortly before Jesus’ birth and was picked up by Christians just after the Crucifixion.

The apostle Paul, for instance, in a letter to Timothy, prayed for divine mercy for his apparently deceased friend Onesiphorus. Likewise, early Christian liturgies and inscriptions on catacomb walls contain prayers for the dead.

The implication quickly sank in: If prayers aren’t needed by souls in Heaven and can’t help anyone in Hell, there must be a third destination. But what?

Barely 100 years after the last book of the New Testament was written, an answer started coming into focus. Theologian Clement of Alexandria theorized that Christians would undergo a purifying fire that “sanctifies . . . [and] penetrates the soul.”

That idea, which was echoed by other writers of the era, might owe some inspiration to Plato, who believed that “curably wicked” souls would endure temporary, “therapeutic punishment” in the afterlife, Bernstein says.

But the Scriptures, too, hinted at post-mortem places other than Heaven and Hades. There was, for example, the question of Jesus’ whereabouts between his death and Resurrection.

“Today you shall be with me in Paradise,” he told a thief who was executed with him. Three days later, however, he said he still hadn’t ascended to the Father. And another cryptic passage indicated that his time in the grave was spent preaching to disobedient spirits “in prison.”

Also baffling was the Gospel of Matthew’s eerie account of dead people climbing out of their tombs and roaming the streets of Jerusalem right after the Crucifixion.

Finally, some verses suggested that Christians wouldn’t be admitted to Heaven until Jesus’ Second Coming. Early believers wondered: Where do the dead go before then?

In the 5th Century, a brilliant North African theologian began mapping out the possibilities. Augustine of Hippo, whose works still influence Catholics (and Protestants), argued that some departed souls await final judgment inside “hidden receptacles” that vary in joy or pain according to how well a person obeyed Christ’s teachings.

Although the name Purgatory wouldn’t be coined for another 800 years, Bernstein says, its basic structure was laid out here.

Strange visions and medieval near-death experiences breathed that abstract framework to life. Often, Purgatory was depicted as a bridge that narrowed or widened in relation to a soul’s merits.

In 717, an English monk allegedly left his body and saw a “way station” near Heaven where the dead crossed a slippery log spanning a river of fire and pitch. Those who hadn’t repented of minor sins fell in, but eventually emerged cleansed on the far bank, according to “Otherworld Journeys” by Carol Zaleski (Oxford, 1987).

In other accounts, Purgatory appeared as a demon-infested valley of fire and ice--or as a fragrant meadow where souls are irradiated by a divine fire that causes paroxysms of ecstasy.

“It’s like a path that goes from the mouth of Hell to the gates of Heaven,” Bernstein says. “Where you’re placed depends on the state of your heart.”

The poet Dante portrayed Purgatory as a mountain, overseen by a guard named Cato (no relation to O.J.’s house guest) and illuminated by a constellation of four flaming stars. Souls traversed the incline carrying weights and battling fire, until they reached Paradise.

Another possible factor in the rise of Purgatory was ghosts. According to Bernstein--who is researching the topic for a sequel to his book “The Formation of Hell”--medieval Europeans were absolutely convinced that unhappy spirits were loose on the continent.

Hordes of the dead were said to be wandering through forests. Others reportedly appeared in cities and homes--even to monks and priests--seeking better burials, sex with former spouses or closure to unfinished business on Earth.

This contradicted the notion that souls went directly and permanently to Heaven or Hell.

Although medieval theologians regarded the sightings as superstitious, it became clear that “there was too much popular resistance to the binary system of Heaven and Hell,” Bernstein says. “There had to be something else.”

In Paris, one bishop taught his clergy to reinterpret the ghost tales. Wandering souls were now said to be on leave from Purgatory to request prayers or charitable acts that would speed their release from punishment.

Over time, such logic put a lid on ghost sightings, Bernstein says.

But Purgatory was hurtling toward trouble.

Even though official Catholic teaching on the matter always stayed vague, in practice it came to be viewed as a hellish prison sentence that could be shortened by donating money to the church.

The sale of indulgences for time off in Purgatory fueled the Protestant Reformation in 1517, which in turn sparked a series of wars between European Christians.

In 1563, Catholics formally outlawed the sale of indulgences. But Purgatory continued to flourish. Even the reformers’ churches had trouble shaking the concept.

Doing away with Purgatory “posed a lasting problem for Protestant theologians,” McDannell says. But periodic moves to restore the doctrine invariably failed.

The classic Protestant argument against Purgatory, aside from the lack of biblical support, is that Jesus’ death eliminated the need for any afterlife redress of sin.

Catholics reply that divine mercy doesn’t exonerate a person from the need to be transformed. Says Kreeft: “If I’m in jail and someone purchases my freedom, the habits of jail are still with me. I have to learn the habits of freedom.”

Some Catholic scholars now speculate that the actual process of dying is Purgatory. Others suggest it’s a spiritual state, not a place.

That’s a dramatic change from the days when clerics searched for the entrance to Purgatory on volcanic Mt. Etna. But the old Purgatory isn’t entirely forgotten.

In an isolated, reddish-brown lake ringed by mountains, the Irish island called St. Patrick’s Purgatory continues to draw pilgrims from around the world. Its renowned cave (which even Shakespeare alluded to in “Hamlet”) was closed in 1780, but that hasn’t stopped visitors intent on a taste of afterlife pleasure and pain.

The three-day ritual consists of a toast-and-tea fast, a 24-hour prayer vigil and a numbing series of barefoot prayer walks along the island’s jagged rock landscape.

Some people have been coming to this anti-Club Med for decades.

When they leave, “There’s a tremendous physical feeling of well-being,” says Msgr. Richard Mohan, the prior of Lough Derg. “People are very conscious of a change in themselves. It’s a great cleansing and detoxification.”

It’s . . . well, Purgatory.