Everything I know about history, I learned at the movies. In the past year alone, I learned-courtesy of the eminent historian Oliver Stone-that Alexander the Great's most formidable obstacle on his way to world conquest was not the Persian army, but his sexy vamp of a mother. Esteemed theologian Mel Gibson taught me that Christ's death and resurrection were not, as earlier scholars like Charlton Heston once believed, "the greatest story ever told," but the world's first snuff film.

Over time, the most important lesson I've learned (other than the fact that everyone in antiquity spoke with a British accent) is that the movies are perhaps not the best place to study history. Ostensibly set in the past, most historical dramas end up telling us far more about present-day values, conflicts, sexual mores, even fashions.

It's to director Ridley Scott's credit that in his new Crusades film, he never pretends otherwise. Kingdom of Heaven opens with the legend "France 1184," but its real setting is our post-9/11, post-American-invasion-of-Iraq present. To Scott, those two worlds are-give or take a few technological innovations like gunpowder and the movie camera-pretty much indistinguishable, and Kingdom of Heaven is his $150-million crusade against religious extremism, be it Christian or Muslim. It's a right-minded movie that is epic in scale but not, sadly, in imagination-at least not in the 2 1/2-hour version now in theaters.

Kingdom of Heaven's early scenes unfold in an earthly hell, a fiery forge where the blacksmith Balian (Orlando Bloom) mourns the death of his newborn son and the subsequent suicide of his grief-stricken wife. A reluctant crusader, Balian journeys to Jerusalem not as a Christian soldier, but as a pilgrim seeking forgiveness-for his wife's suicide (which, according to church doctrine, consigns her soul to hell) and for the crime he commits in her name.

Atonement is also on the mind of Balian's long-absent father, Godfrey, Baron of Ibelin (Liam Neeson, in a brief but affecting performance), a knight who abandoned Balian's mother before their son's birth to join the Crusades. "I have forgiveness to ask of you," Godfrey tells Balian, and in exchange he offers his son not only his title, but more importantly, a moral code to live by: "Be without fear in the face of your enemy. Be brave and upright that God may love thee. Speak the truth even if it leads to your death. Safeguard the helpless, and do no wrong."

For Scott and his screenwriter, William Monahan, this knight's oath of "right action" is far more compelling than any religious doctrine or political ideology-and far less corruptible. After Balian arrives in Jerusalem and assumes a position of leadership, he discovers his real enemies are not necessarily the Muslims, but power-hungry Christian noblemen bent on provoking a war with the Muslim leader Saladin (played with great dignity by Syrian actor Ghassan Massoud) and hypocritical clergymen who sanction the acts of terrorism required to do so.

To drive home their point that every faith is capable of using God's name to sanction acts of unholy violence, Scott and Monahan take words and deeds that contemporary audiences will associate with one faction and give them to another. "To kill an infidel is not murder; it is the path to heaven" is uttered not by a radical Muslim cleric but by a Christian priest blessing crusaders preparing to sail for the Holy Land. The first beheading-there are many-is ordered by a Christian; the rush to war is led by a Frenchman. And when an army unleashes a campaign of shock and awe against a city filled with civilians, it is the Muslims laying siege to Jerusalem.

Amid such chaos, Scott suggests, "right action" and military victory are not necessarily the same thing. Charged with leading the defense of Jerusalem, Balian pursues a course that would make him an outcast in a different film, not to mention the Bush administration. Kingdom of Heaven, by contrast, regards him as a hero, as it does those Muslim leaders who are as ready to wage diplomacy as they are war.

Yet if Scott wins the battle of ideas, he loses his fight to make a truly memorable film. Too often, Kingdom of Heaven feels like a 300-year crusade compressed into a single long weekend-or rather, like a greatly truncated version of the almost four-hour movie it originally was (and will be again on the DVD). Few individual scenes are afforded the time they need to develop, and major set pieces, including a dramatic shipwreck sequence, are reduced to mere flashcards.

Thanks to his roles in the Lord of the Rings trilogy and Troy, Orlando Bloom is no stranger to epic filmmaking, and like Eva Green (who plays Balian's love interest, Sibylla), he is certainly a thing of beauty. But he lacks both the physical and emotional heft that Russell Crowe brought to Scott's Oscar-winning Gladiator, which gave that film an excitement and a resonance that Kingdom of Heaven can't match. Given his powerful message (and a r??sum?? that includes Alien, Blade Runner and Thelma and Louise), you wish Scott had fulfilled his own knight's oath and made a better movie. Instead, he demonstrates just how difficult it is to do the right thing-even when the field of battle is only Hollywood.