It has been 13 years since the 9/11 attacks on the US in which almost 3,000 people were killed.
In New York, where the twin towers of the World Trade Center were destroyed, a new skyscraper has risen from the ashes of Ground Zero.
Irish artist Marcus Robinson has spent the past eight years filming the transformation, and his documentary Rebuilding the World Trade Center will be broadcast in the US on 11 September on the History Channel.
The BBC's Laura Trevelyan has more on this artist's labour of love.
Filmed and edited by Stephen Greaves
