Credit must be given to Alejandro Amenábar's uncharacteristic and unexpected costume drama Agora for being rather more thoughtful than the average sword 'n sandal epic. Thoughtful, you might say, to excess. If there's one thing that's eminently clear about the script that the director co-wrote with his regular collaborator Mateo Gil, it's that the two men have Something To Say About The World In Which We Live. Earnestness is not the worst thing that can happen to a movie, especially one that is made with such handsome attention to detail in the creation of one of the most fully realised, living and breathing environment in any movie I've seen in theaters this year. But goddamn, Agora is earnest and then some. It plays very much like an incredibly sincere episode of Moments in History for Lil' Atheists, which is certainly a an idea that I can get behind; yet it would be better to have a bit less history lesson and a bit more dramatic momentum.

It is 391 CE, in the Egyptian city of Alexandria. There, at the world-renowned library, where scholars work to collect all the knowledge of humanity, a woman named Hypatia (Rachel Weisz) studies mathematics and the structure of the world, teaching a class of rapt pupils about the Ptolemaic system thought to guide the paths of the planets and stars, following in the steps of her great father, the director of all the Musaeum (including the library), Theon (Michael Lonsdale). Reason and rationality are king there; but outside the walls, the city of Alexandria is torn apart by the tension then gripping all of the tottering Roman Empire, between ancient pagan religions, and the saucy upstart Christians, who have lately been made the official imperial religion. Hypatia would rather not have anything to do with the religious conflicts, but she has little choice in the matter, and before too long, the temple to the pagan god Serapeum, located on the library grounds, is under assault by a Christian mob. This ends very badly. Famously badly, you could even say, for the short-sightedness and venality of both sides in the conflict leads by turns to the near-complete destruction of the most priceless collection of human wisdom in history.

So far, mostly so good. The film is over-eager to present ideas, which means a lot of talking and demonstrating and talking about the demonstration, but there's something wonderful about a movie that so wantonly celebrates reason above all else. Amenábar rather goes out of his way to pick bad guys: for every crazy Christian there's a wicked pagan, and reasonable people can be found on both sides as well (though in much smaller number). Agora does not reflexively bash anyone in its first half, but gives all participants equal blame, and, when it's due, credit.

Mostly, though, the film is a massive love-letter to Hypatia, an historic figure whose writings have all been lost, except in fragments quoted by other thinkers. Even so, we do know that she was one hell of a person: the first important woman philosopher (the old-timey word for "scientist") in recorded history, at a time when women weren't meant to be allowed to think at all, whose studies remain, in some respects, tremendously valuable even today. Most of Hypatia's personal history has been lost to time, and much of Agora can be regarded as bunk (it is virtually impossible to imagine that she was quite so rigorously atheistic as the film anachronistically suggests), but whenever possible, Amenábar and Gil use the scant available historic details to serve as the base for everything they present.

Factually sound or not, Agora certainly has a high opinion of its version of Hypatia, a beacon of intellectual fortitude and conviction. In this telling, it's not hard to see why three of her students, including the Christian Synesius (Rupert Evans), known to have studied under her, the pagan Orestes (Oscar Isaac), who may have studied her and certainly knew her in later years, and the fictitious slave Davus (Max Minghella), all fall head over heels in love with her: she's effectively perfect. And it's also not hard to understand why she gently refuses to fall in love with anyone: she's effectively perfect. The role gives Weisz a great many opportunities to play up both her strengths and her weaknesses, which often shade into the same thing: a breathy sincerity in which her whole body, from her gleaming eyes on down, radiate the certainty that whatever she's saying at this moment is the very most important thing ever spoken by any human being. At times, this approach - to say nothing of the screenplay - makes it kind of difficult to take Hypatia especially seriously as a person, but when the film clicks just right, her overloaded enthusiasm brings to life the perspective, advocated by such luminaries as Carl Sagan, that unabashed wonder is the only appropriate response to the impossible grandeur of the universe revealed by scientific discovery. This perilously-balanced characterisation has its dangers, but it more or less works given Amenábar's obvious aims: the corniest scene in the movie is also the most thrilling, in which Hypatia discovers that the planets move in elliptical orbits around the Sun. "An ellipse!" orgasms Weisz, and as silly as it sounds (and is), there's no doubt that it gets across exactly the kind of awe that it's supposed to. Besides, it's kind of amazing that any film would make its emotional climax the discovery of elliptical orbits. Even if positioning Hypatia as the discoverer of the heliocentric model of the solar system strains historic credibility to the snapping point.

So anyway: the first half of the movie is a desperately sincere paean to Reason rising above the petty political and religious squabbles of culture. The second half is that, with a whole lot of "and by the way, fuck the Christians" thrown in. By no means am I anything like a Christian. And the expression of the very well-founded idea that first-millennium Christianity was responsible for some diabolically wretched insults to the intellectual development of humanity should offend no-one with a decent history book at their disposal. But, having carefully refused to make any particular individual a stereotype of any sort of believe, the second half of Agora, set "several" years after 391 (Hypatia died in 415, so it's probably a year or two before that), introduces a full-on mustache-twirling villain in the form of Cyril (Sami Samir), Pope of Alexandria. A conniving politician who uses religious dogma to sweep away all of his opponents and turn the city into his private dictatorship, Cyril is, perhaps, no worse than the historic figure (Saint Cyril of Alexandria, now counted among the Fathers of the Church, was decried as a demon and heretic even in his own time for his acts of violence). But he certainly imbalances the movie. It is entirely possible that there would be no way to tell the story of Agora without this kind of Evil Religious Fanatic to anchor the drama; nevertheless, it would be eminently possible to do all this without turning the second half of a rather long movie (127 minutes) into a non-stop harangue.

Thus: two hours of talking about ideas that can't really be dramatised because of their theoretical complexity, plus a good old-fashioned pile of "I AM TELLING YOU A MESSAGE, DO YOU UNDERSTAND THAT FUNDAMENTALISM IS DANGEROUS?" lecturing, and so Agora ends up a bit draggy. Which is a shame, because all of the ideas and themes it puts forth are fascinating and could be quite enlightening for the modern age, if the film they were attached to was even a tiny bit fun to watch. But not for Agora anything like "entertainment"; it is Serious.

Nevertheless, it presents some good eye candy. Amenábar snagged the wonderful Guy Dyas to do the film's production design, and Gabriella Pescucci for the costumes (the two designers worked together before, incidentally, on Terry Gilliam's lovely but dramatically void The Brothers Grimm), and what they put together is nothing shy of marvellous. Alexandria as depicted in this film is one of the most exquisitely-realised ancient cities ever put to film, a character as vital - if not more - as any of the human figures we see. Created largely practically, with CGI used only out of necessity, it's wonderfully textured and tangible, luscious and utterly real. Amenábar and his cinematographer, Xavi Giménez, frame the city to its best effect, and from time to time the director indulges in a cheesy but well-meant effect, swooping all the back into space to show us Alexandria's position in Egypt, Africa, the world, the universe - for all that it's thematically hamfisted, it's visually thrilling, and the match from the CGI zooms to the practical sets is seamless.

If only the jaw-dropping beauty of Agora were married to a film that had as much room to breathe as the sets! But no, this is to be a time for a lesson, and not the time for fun. Obviously "fun" isn't the single reason why any movie should exist, but Amenábar should have taken hints from his own depiction of Hypatia: she certainly understands that a lesson in which you thrill and engage and involve your students will always be more effective than one in which you stand in front of them and inform them, "this is how things are, and you don't get to doubt me, because I'm the one with the movie camera". A great movie lies just under the skin of Agora, but its flaws are damned hard to ignore.