War and romance often make excellent cinematic bedfellows, but who can say why? Maybe it’s the fact that these two implacable impulses somehow exist in spite of each other; in the words of maverick dramatist Bertolt Brecht, the fact that both “always find a way.”

In “A Very Long Engagement” — starring Audrey Tautou as a French woman who braves bureaucrats, Corsican assassins and polio-ridden legs to locate her lost fiance in the chaotic aftermath of World War I — filmmaker Jean-Pierre Jeunet (“Amelie”) mingles the horror of battle with the bliss of romance to create the most vivid and moving wartime love story since “The English Patient” (1996). It’s a vast, sublime fresco of tragedy, humor and faith, delivered with the filmmaker’s singular wit and visual flair.

Tautou, as waifish country girl Mathilde, plays a character similar to her “Amelie” heroine: spirited, superstitious (she has a thing for four-leaf clovers) and prone to epic flights of fancy. She is not, however, in the match-making business; when the French army informs Mathilde that her fiance, Manech (Gaspard Ulliel), perished under mysterious circumstances in the trenches of the Sommes — but can produce no corpse — she drains her inheritance and goes looking for him. Sniffing for clues, she picks up a trail of squelched loves and ruined lives. Jodie Foster, in her French-language debut, gives a raw, moving performance as a lonely woman who had an affair with one of Manech’s fellow soldiers.

Piecing together the events that led to her fiance’s demise, Mathilde uncovers a sordid tale of corruption and kangaroo court justice apparently inspired by filmmaker Stanley Kubrick’s war classic “Paths of Glory” (1957). Jeunet — an unapologetic fabulist whose credits include “Alien: Resurrection” and “The City of Lost Children” — fills the margins with a parade of horrible, haunting images: burning soldiers being riddled by bullets from their own exploding ammo clips, shell-shocked grunts shooting themselves in the hands for a free ticket home and a crazed officer kicking corpses, exhorting them to get up and fight.

Jeunet doesn’t always find a perfect use for these images — some audiences will surely find the violence gratuitous — but like Terry Gilliam (“12 Monkeys”) in his best moments, neither does his showmanship smother the story’s soul. Ultimately, Jeunet generates just as much power from the image of two people embracing as killing each other, and with Tatou as his Tinkerbell, conjures an adult fairy tale for the ages.