One has the success of “Gladiator” to thank, or blame, for the revival of the toga-and-sandal epic, of which Wolfgang Petersen’s super-sized retelling of “The Iliad” (or more properly, the whole Trojan war tale of which that text is the most important part) is one of the first fruits. The Homeric poem and its addenda have a long cinematic history, reaching back to Giovanni Pastrone’s “La Cadusta di Troia” in 1911, but the only consequential past treatment was Robert Wise’s 1956 “Helen of Troy.” (One can certainly dismiss the two Italian efforts from 1962–“The Fury of Achilles” and “The Trojan Horse”–neither of which transcends the limitations of their Steve Reeves “Hercules” roots.) Wise was a conscientious craftsman, and his wide-screen, cast-of-thousands picture reflected the fifties’ taste for large-scaled adventure tales about the ancient world. But it was stilted in the peculiarly pseudo-Shakespearean way affected by the studios in their epics of the period, and it transformed what is, after all, essentially a story about a warrior’s rage into a sappy, doomed romance concentrating on Paris (its hero) and the beauteous Helen. (The recent USA miniseries of the same name did likewise, but in a far more soapoperatic way.) Its only really interesting oddity was that it offered the aging Sir Cedric Hardwicke the opportunity to sit on two royal thrones in a single year. He was Priam, the elderly king of Troy, in Wise’s film, and in Cecil B. DeMille’s “The Ten Commandments,” also released in 1956, he played the Egyptian pharaoh.

Petersen’s huge effort overshadows Wise’s in terms of both scale and effects. And “Troy” certainly boasts a far starrier cast. For Paris, there’s Orlando Bloom instead of Jack (actually Jacques) Sernas (who?), and for Achilles it offers Brad Pitt in the place of Stanley Baker. Harry Andrews (Hector) is replaced by “Hulk” star Eric Bana, and Hardwick by Peter O’Toole. Instead of Niall McGinnis and Robert Douglas as Menelaus and Agamemnon, meanwhile, we get Brendan Gleeson and Brian Cox. Even Julie Christie shows up briefly as Achilles’ divine mother Thetis. (Of course, as yet the Helen, Diane Kruger, isn’t much better known than Rosanna Podesta–who?–was in 1956.)

But the major question isn’t the name recognition of the players, but the quality of the material that screenwriter David Benioff (“The 25th Hour”) has provided them with. Unhappily, it’s not terribly high. One can’t expect absolute fidelity to “The Iliad,” of course: the poem embodies an idea of virtue that would be pretty much incomprehensible to modern moviegoers, and structurally–dealing with a single incident in the tenth year of the war–it simply couldn’t stand on its own. So while one might complain of all the alterations Benioff has made–jettisoning all the stuff about the gods to make the film a purely human story and turning Homer’s decade-long siege into an enterprise that’s apparently completed over the course of a couple of weeks, for instance–one has to at least congratulate him for keeping the focus on Achilles, where it belongs, and retaining, in sporadically effective form, quite a few of the most famous episodes from the poem. In fact, “Troy” is at its best when it sticks to the text, as it were, most often when it revels in scenes of battle, just as Homer did. The initial clash outside the walls of Troy, for example, is pretty impressive: it might look a lot like the big battle scene from “Spartacus” and sound a bit like the Prokofiev of “Alexander Nevsky” (one of the few instances in which James Horner’s score breaks free of its generic drums-and-trumpets cliches), but those are good models to imitate. And the man-on-man combat scene between Achilles and Hector is extremely well-done, so fine in fact that it calls to mind another great moment from “Spartacus”–the duel between Kirk Douglas and Woody Strode in the arena. The other action scenes in the first three-quarters of the long (162-minute) film are splendidly staged, too, even when (as in a prologue dealing with Agamemnon’s takeover of Thessaly, or an initial battle for the beach outside Troy), they’re not strictly Homeric. The single highlight of “Troy,” however, comes in a far more intimate scene that Benioff takes almost directly from Homer, the face-to-face meeting between Achilles and Priam following Hector’s death, in which the aged monarch comes to the warrior’s tent to appeal for his son’s battered body; what might have been mawkish is redeemed by O’Toole’s grave dignity–it’s one of those instances in which the audience responds not just to an actor’s immediate performance but to the career accomplishment that lies behind it.

But when Benioff takes off on his own, especially in terms of appealing to contemporary taste for emotional sensitivity and easy resolutions, “Troy” goes off the rails. He doesn’t make the mistake that Wise (and his scripters, John Twist and Hugh Gray) did, of showcasing the romance between Paris and Helen. Indeed, those two characters are distinctly secondary, with Helen in particular being relegated to the sidelines. (Paris, on the other hand, has a couple of center-stage moments, but for the most part he’s depicted as a sort of playboy wimp, especially when he cowers during a one-on-one with Gleeson’s Menelaus. Even toward the close, when he takes up bow and arrow in suddenly heroic guise–an amusing moment, given how much it calls to mind Bloom’s turn as master archer Legolas–the prince is out of his depth.) But Benioff makes a similar mistake by “humanizing” Achilles and Hector with an over-emphasis on their romantic attachments. The matter isn’t serious on the Trojan side, because Bana is so good as Paris’ older brother–effectively portraying a conflicted man with a fatalistic streak–that even Peterson’s insistence on using entirely too many inserts of his infant son Astyanax and the worried face of his wife Andromache (Saffron Burrows) doesn’t seriously detract from the strength of the performance. With Achilles, on the other hand, the matter is different. In Homer, the warrior’s major attachment was to his own honor and to Patroclus, his closest friend, played here by Garrett Hedlund (whose striking physical similarity to Pitt certainly helps one plot turn). Benioff has transformed Patroclus into Achilles’ cousin–a blood relationship non-existent in Homer, where the connection between the two men isn’t based simply on kinship or even military camaraderie, but something deeper. (That’s one aspect of ancient Greek culture that many American moviegoers probably couldn’t handle, so one can perhaps accept Benioff’s alteration.) But then, to demonstrate that Achilles was a real man’s man in the modern (rather than the ancient) sense, and to preserve Pitt’s image no doubt, he invents a tragic romance between Achilles and the Trojan captive Briseis (Rose Byrne), who’s mostly a footnote in Homer–the incidental catalyst to the rage the warrior feels against Agamemnon–but who becomes here the agent of Achilles’ transformation from a vainglorious machine of death into a sensitive fellow who will move heaven and earth to see that she’s protected. The change brings to “Troy” the same element of sappiness that afflicted Wise’s film, just from a different angle (as well as Lifetime-caliber lines of dialogue, as when Briseis tells the unclothed Achilles after they’ve slept together, “Last night was a mistake”). And it leads inevitably to the film’s fatal final half-hour, dealing with the actual fall of the city, which is not only staged surprisingly poorly (it looks claustrophobic and messy), but involves a wholesale rewriting of the traditional circumstances of Achilles’ death that embraces the conventions of modern melodrama more than those of ancient epic. One can point to other changes wrought by Benioff that cheapen things, too. The fates of Menelaus and Agamemnon, for example, seem calculated to appeal to modern viewers’ demand for immediate emotional gratification: brutes have to get their comeuppance, no matter what storytelling extremes, utterly at variance with Greek myth, one might have to seize upon to give it to them. (The sad thing is that it’s not necessary. Even Mel Gibson didn’t feel the need to kill off Edward I unhistorically in “Braveheart.” Here it’s literature rather than history that’s insulted, but when it’s ancient Greek literature the offense is nearly as great.) And a bit of business about “the sword of Troy” being bequeathed by Priam to Paris, and by him in turn to the youth Aeneas as he flees the burning city, really takes one into comic-book territory. (Of course, in Homer Aeneas isn’t some callow youth but a strapping warrior.) But happily, at least the fate of Paris and Helen isn’t explicitly shown by Petersen, because one can be sure doing so would have taken us to a whole new level of embarrassment.

Still, in spite of its narrative shortcomings, “Troy” emerges as an ambitious epic, handsomely mounted (excellent widescreen cinematography by Roger Pratt, and an interesting production design by Nigel Phelps that mixes together ancient Near Easteren and medieval elements) and (apart from the final section) expertly directed. Bana and O’Toole are the standouts in the cast, both connecting emotionally with an economy of means. Pitt brings to his role his natural good looks–the fact that he could probably stand in for a Greek god makes Petersen’s almost fetishistic concentration on his partially disrobed body almost acceptable–and he’s strikingly good in the action scenes. In the smaller moments, though, he doesn’t measure up. His anger comes across as more modern petulance than Homeric hubris, and the conversational interludes show his deficiencies even more cruelly (especially when he’s talking with O’Toole, in their single scene together, or with Sean Bean, who makes a fine Odysseus, even if the sequence in which he gets the idea for the horse has a ludicrous “light bulb” feeling to it). Cox and Gleeson, good actors both, are unfortunately given little opportunity to add shading to their scowling, grumpy Greek kings. And in this company Bloom appears all too convincingly as a weak, thoughtless youngster. The women in the cast, unhappily, have relatively little to do but model attractive dresses and look appropriately distressed over the outcome of the fighting. The world of the ancient Trojan cycle was, after all, a man’s one, unless one moves into the realms of Greek tragedy, where a Clytemnestra emerges and Agamemnon truly gets what he deserves.

So for two hours or so, “Troy” is a reasonably good boys’ adventure story–a sort of Classics Comics version of Homer and his successors, perhaps, but one with some visceral punch. In the final act, however, it goes haywire, Benioff and Petersen bungling things so badly that the picture practically descends to the level of “Saturday Night Live” parody. Once Pitt was cast as Achilles, perhaps it became necessary to keep the character alive to the end and give him a sloppily histrionic sendoff, but if so, it would have been better not to cast him in the first place. The upshot of the miscalculation is that, unlikely as it might seem, the best modern version of a Homeric epic remains the Coen brothers’ American refashioning of “The Odyssey”–“O Brother, Where Art Thou?” Faithful? Even less than Petersen’s picture. But a great movie? Absolutely. Unfortunately, the only way in which “Troy” is great is in terms of physical size; as a drama it’s only a modest improvement on Wise’s 1956 entry–and in the final half-hour, not even that.