On the morning of September 11, 2001, brothers Jules and Gedeon Naudet were working on a documentary about a rookie New York City firefighter.

Hearing a roar in the sky, Jules turned his camera upward - just in time to film the only existing image of the first plane crashing into the World Trade Centre.

In a fateful instant, Jules and Gedeon became eyewitnesses to the most shocking and defining moment of our time.

With cameras rolling, the Naudets followed NYC firefighters into the heart of what would be known as Ground Zero.

What emerged is an unforgettably powerful visual document and a stirring tribute to real-life heroes who, in their citys darkest hour, rose to extraordinary acts of courage and compassion.