The silver spire topping One World Trade Centre has been fully installed on the building's roof bringing the landmark structure to its full, symbolic height of 1,776 feet
Pieces of the spire were transported to the roof of the building last week. It weighs 758 tons.The 408-foot spire will serve as a world-class broadcast antenna.
An LED-powered light emanating from it will be seen from miles away.
The new tower is at the north-west corner of the World Trade Centre site, which is well on its way to reconstruction with the 72-storey Four World Trade Centre and other buildings.
The 1,776 feet - or 541 metres - is symbolic of the year 1776, when the US declared its independence.
The north-west corner of the site is where the twin towers were destroyed in the Sept 11, 2001, terror attacks.
The addition of the spire would make One World Trade Centre the tallest structure in the US and third-tallest in the world, although building experts dispute whether the spire is actually an antenna - a crucial distinction in measuring the building's height.
If it didn't have the spire, One World Trade Centre would actually be shorter than the Willis Tower in Chicago, which stands at 1,451 ft (442.26 metres) and has the title of tallest building in the US, not including its own antennas.
The Council on Tall Buildings and Urban Habitat, a Chicago-based organisation considered an authority on such records, says an antenna is something simply added to the top of a tower that can be removed. By contrast, a spire is something that is part of the building's architectural design.
The tower is slated to open for business in 2014.