Since planners began the process of deciding what will replace the World Trade Center buildings destroyed on Sept. 11, 2001, a tempest of criticism and indecision has swirled around the site. Nonetheless, after five years, construction has begun.

Numerous projects are under way at the site of the new World Trade Center, where all original seven buildings, including the twin towers, were either destroyed or demolished because they were irreparably damaged.

The new site will house a memorial, five buildings, and a transit hub designed, according to World Trade Center officials, to accommodate 250,000 daily commuters and visitors by 2020.

In 2003, the Lower Manhattan Development Corp., the agency in charge of coordinating the reconstruction of Lower Manhattan, chose renowned architect Daniel Libeskind -- a naturalized U.S. citizen originally from Poland and the son of Holocaust survivors -- and his master plan for the larger site, titled "Memory Foundations."

Many revisions ensued with much of the attention zeroing in on Freedom Tower, the 1,776-foot skyscraper that will replace the towers in New York City's skyline, and a memorial at the tower's foot. The structure is intended to document the events of the day and commemorate the people who died at the attack site, not only on Sept. 11, 2001 but also on Feb. 26, 1993 when a truck bomb exploded in the garage of the North Tower, killing six people and injuring some 1,000.

Libeskind in 2003 envisaged a soaring, abstract structure with windmills, an aerial garden and an off-center spire meant to evoke the Statue of Liberty.

Changes came when Libeskind and David Childs, another architect hired by site leaseholder Larry Silverstein, worked together in "a gritted-teeth collaboration between two architects whose styles couldn't be more different," according to the architecture editor for the Los Angeles Times.

After the New York Police Department cited security concerns over the proposed building, yet another design was unveiled in 2005. Barring unforeseen circumstances, this design will be the structure that will be built by 2011.

All told, the 2.6-million-square-foot Freedom Tower is expected to cost $2.1 billion.

The exterior of the building is an obelisk, a tapered four-sided pillar, with its edges cut away diagonally. A rooftop parapet will be 1,368 feet above street level -- the same height of the former North Tower. From there a spire will rise to a height of 1,776 feet, marking the year the United States declared its independence from Britain and making it the tallest building in the country.

Office space and restaurants will inhabit the Freedom Tower, as well as an observation deck on the 102nd floor, containing plenty of security.

A state-of-the-art emergency system and extra-wide staircases will be installed, but the building's most conspicuous security enhancement will be its base: a 200-by-200-foot concrete pedestal measuring 20 stories in height.

When the design was first introduced, many critics argued that the base, while effective at absorbing forces such as truck bombs, would be uninviting for people walking by at street level. To solve the problem, Childs proposed covering the base with a screen of glass prisms. If broken, the laminated glass would simply crumble into tiny pieces.

Nicolai Ouroussoff, the architecture at The New York Times, blasted the building's form last year, calling it "an impregnable tower braced against the outside world."

"If this is a potentially fascinating work of architecture, it is, sadly, fascinating in a way that Albert Speer's architectural nightmares were fascinating: as expressions of the values of a particular time and era. The Freedom Tower embodies, in its way, a world shaped by fear," he wrote.

Similar quarrels over aesthetics have plagued the World Trade Center Memorial -- to be located near the foot of the Freedom Tower.

Named "Reflecting Absence," the memorial was designed by Michael Arad, whose plan was chosen out of move than 5,000 submissions from around the world.

The plan calls for two square-shaped voids in the footprints of the original twin towers. The voids will be filled like pools, with waterfalls and oak trees on all sides. The names of the victims who died on Sept. 11, 2001 and Feb. 26, 1993 will appear on a wall surrounding the memorial.

Adjacent to the memorial will be the Memorial Museum. Its purpose is to document the day with powerful -- and at times, graphic -- artifacts.

The memorial and museum are slated to be completed in September 2009.

In July 2006, the Port Authority of New York and New Jersey assumed control of building the memorial and museum, as well as the site's visitor center and education center. The World Trade Center Memorial Foundation, a nonprofit company designed to raise funds and oversee planning for the 16-acre memorial site, will maintain and run the memorial site once it is built.

Construction on the footings for these structures began in August 2006 -- much like the Freedom Tower, only after intense debate.

In early 2006, building officials said the memorial site would cost nearly $1 billion -- a price that provoked outrage from New Yorkers. In response, New York Gov. George Pataki and New York City Mayor Michael Bloomberg slashed the budget in half.

There also were questions about the museum's location and about whether a culture center, the International Freedom Center, was an appropriate addition to the site. Officials eventually scrapped the idea.

Another debate was triggered by the way the names of the victims would appear on the memorial.

According to Debra Burlingame, a board member at the World Trade Center Memorial Foundation, the names will be "randomly sprinkled" about -- abiding by Arad's desire to express the randomness of death. But she thought the names should be grouped by association.

"They didn't die randomly," she said. "When [people] hear that someone died at the World Trade Center, they ask two things: Where were they and how old were they?"

Nonetheless, Burlingame, whose brother piloted American Flight 77, which terrorists crashed into the Pentagon on Sept. 11, said she has "great hopes" the site will be well-attended. She said 1 billion people are expected to visit the memorial each year.

"We know that before Sept. 11, the Statue of Liberty got 5 million visitors a year, so we're thinking at least 5 million a year, but certainly more," she said.

-- By Oliver Read, Online NewsHour