5 September 2011 Updated at 18:42 ET
9/11:
How New York's twin towers were built
The 110-storey landmarks that dominated the Manhattan skyline for nearly 30 years were reduced to rubble in the 9/11 suicide attacks of 2001. Thousands of people in the World Trade Center, and on the planes that crashed into them, lost their lives.
link-
http://www.bbc.co.uk/news/magazine-14634600