Pictured: The World Trade Centre site seven years after 9/11

Work goes on 20 hours a day here, in a section of the 16-acre site known as the ‘east bathtub’.

The two cranes that dominate this urban landscape are in place to install the steel foundation columns of 1 World Trade Centre, or ‘Freedom Tower’ – the main building of the new WTC.

To the right of the cranes, at street level, a mixer pumps concrete down a navy-blue funnel into the bathtub. The concrete will be used to construct the tower’s core.

Men at work: The 'east bathtub' site

The West Side Highway, with its six lanes of vehicles, separates the construction site from the four World Financial Centre skyscrapers. And you can just glimpse the Hudson River through a gap between two of the buildings.

A wide road has been built from street level to the heart of the construction site, allowing up to 100 36-ton dump trucks to access the bathtub daily.

After nearly two years of heavy excavation, more than half a million tons of soil, rock and debris have been removed and there are still thousands more to go.

An architectural landmark for New York City, the Freedom Tower will soar 1,776ft skyward to become America’s tallest building.

The 2.6million sq ft edifice will include office space, an observation deck, restaurants and broadcast facilities and antennae. It is scheduled to open in 2011 – to mark the tenyear anniversary of the terrorist attacks that destroyed the original World Trade Centre.

Three other high-rise office buildings and a residential tower are also planned. They will surround the World Trade Centre Memorial, which is currently under construction. The area will also house a museum.

Iconic: Hijacked United Airlines Flight 175 from Boston crashes into the south tower of the World Trade Centre at 9:03 am on September 11, 2001