Aspects of the film are strongly reminiscent of Tolkien, or on-screen Tolkien. It is not that Lewis stole walking trees from The Lord of the Rings (though before he wrote Prince Caspian he had heard Tolkien reading from his books). After all, a moving wood figures in Macbeth. The difference is that Lewis imagined what a hamadryad from classical mythology would be like. Tolkien imagined a whole mythology.

Lewis's approach comes out clearly in a lengthy scene in Prince Caspian that the film-makers did not dare include: a corybantic romp by Bacchus and his Maenads, with Silenus on his donkey (conventionally depicted elsewhere with a giant phallus, as, surprisingly, on the Victorian cover of Punch magazine each week). In something of an understatement, Susan remarks in the book: "I wouldn't have felt safe with Bacchus and all his wild girls if we'd met them without Aslan."

Yet Bacchus, or Dionysius, as well as being a mythic god of drunkenness, is as clearly an off-the-shelf figure of Jesus Christ as Lewis's invented Aslan. Lewis as a classical scholar was fully aware of the mythic power of Dionysius.

"I am Dionysius, the son of Zeus," the man-god declares at the beginning of Euripides' play, The Bacchae. "I have put off the god and taken human shape."

Instead of daring these complications, the film prefers to insert a long battle scene not in the book, expanding its duration to two-and-a-half hours of clangorous Dolby Digital. I'm not sure Lewis would have cared for that.