On August 7, 1974, Philippe Petit approaches the steel precipice of the South Tower of the World Trade Center, where a thin tightrope lay fixed. “This is probably the end of my life,” he thinks. But, “something that I could not resist called me upon that cable.” And so he walks, alone, without safety nets or harnesses, onto the void nearly 1350 feet off the ground. His face is ghastly pale and shows pain, “an ageless mask of concentration,” as taut as the 200-foot cord upon which he balances. With a sharp nose turned upward, his eyes pierce a few steps ahead of him with imperturbable focus, studying the cable. He moves slowly, gingerly across. Suddenly, his expression releases its tension and begins to exude sheer ecstasy. “Now, I am going to perform,” he thinks.

For forty-five minutes, he remains on the cable with unrelenting stamina, making eight passes, balancing pole in hand. At one point he salutes his audience, at another he kneels majestically like a king surveying newly conquered territory, and then he alights softly like a swallow, lying down, his pole forming a perpendicular angle with the cable. It is an exercise in meditation — an art, beautiful in its simplicity, spiritual in its impossibility.

Why do it? We watch in wonder as he teeters on the thin line between life and death. The question is as inscrutable as the answer. When asked, Petit mysteriously replies: “There is no why.”

First released at the 2008 Sundance Film Festival, where it won the coveted Grand Jury Prize, “Man On Wire” is the mystically simple, awe-inspiring story of the man, the mission and the question that underlies both.

The film takes the form of interviews with Petit, his accomplices and friends, real-life footage documenting his evolution into the world’s most infamous tightrope con man, and a black and white fictionalization of the events preceding the World Trade Center attempt. Director James Marsh skillfully moves back and forth between these three, building suspense and leaving the interviewees to take responsibility for all the narration, which nevertheless adheres organically with both the professional acting and the documentary photographs and film. Petit, now nearing 60, maintains his youthful eccentricity, narrating to us in idiosyncratic English tinged by his heavy Gallic accent.

From the fields of rural France, Petit takes his self-taught ambitions with him to Paris, where he tightropes the Notre Dame after a year of preparation, and a year later the Sydney Harbor Bridge. Above Notre Dame, dozens of priests lie with heads against the floor, in prayer, staggered and dumbstruck by his almost religious sublimity. The image is otherworldly. The rest of the film focuses on the details — most interesting, some unnecessary — of both the plans to scale the World Trade Center and their realization.

From the ground looking up, Petit, dressed in black bell-bottoms fanning in the wind, dancing between the two towers, the wings of his balancing pole pointing outward on each side, is a dark, looming angel. As he hovers there on screen, the unmistakable omission of any reference to the towers’ future fate — an image inescapable from the minds of anyone in the audience — is all the more prominent. Above all else, it is the juxtaposition of these two images on screen and off, of triumph and of ruin, of August 7, 1974 and of September 11, 2001 — this haunting, yet magnificent synergy of the transcendent and the real — that anchor in the viewers’ mind, making the film unforgettable.