The 57-ton staircase was moved by crane across the trade center site to the future entrance of a museum commemorating the 2001 terrorist attacks.
The stairs were moved from from their original spot at the trade center site in March - after construction crews chipped away at the concrete foundation and replaced it with metal supports. Another leg of the journey was completed in July.
The 37 stairs had stood for years as the last remaining above-ground remnant of the original trade center complex.
Preservationists - and survivors who used the staircase to get quickly from the trade center complex to the street below on Sept. 11 - had battled to see it preserved in some way. One group put it on a list of the nation's most endangered historic places.
Eventually, the stairs will be part of the entrance pavilion to the below-ground museum, expected to open in 2012. Visitors won't be able to use the stairs but will see them as they descend a parallel stairway from street level into the museum.
A battle for their preservation was touched off after state officials announced in 2006 that all but one or two slabs of the staircase would be demolished to make way for the new tower being built on the site. Planners changed their minds a year later, finding a spot for the stairs at the entrance pavilion to the below-ground memorial museum.
The staircase weighed 175 tons at the time, too heavy to drive across bridges into storage; officials couldn't find space for it in a nearby park. Preservationists had initially hoped it would stay in the same place, but it stood in the footprint of one of five planned office towers.