On Monday morning, businesses, such as publishing giant Conde Nast, began moving into One World Trade Center, the 104 story skyscraper that is now America’s tallest building.

It stands in the centre of a 16 acre site where the twin towers were once located, and where 2,700 people died in 2001 after two planed struck the buildings in which they worked.

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The tower overlooks the National September 11 Memorial & Museum, which was built in the footprints of the buildings that were lost.

Port Authority executives have apparently called the site ‘the most secure office building in America.’

At present, only employees are allowed in and out of the office block, but eventually an observation deck will be open to the public, allowing them to take in the stunning views of New York city.

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New York Governor Andrew Cuomo said: ‘One World Trace Centre serves as a symbol of the resilience of the people of New York.’

‘We remember that strength and courage will always conquer weakness and cowardice, and that the American spirit, defended by proud New Yorkers, will not be defeated.’

The Wall Street Journal reported: ‘The New York City skyline is whole again.’

Since the horrific attacks on September 11, 2001, the area surrounding the twin towers has flourished, with businesses being bolstered by an extra 60,000 people living in the area.