Plans for the National September 11 Memorial and Museum at the World Trade Center were announced in early 2004, unveiling architects Michael Arad and Peter Walker’s design, “Reflecting Absence.”

Intended as a solemn space where visitors can remember and honor the thousands of lives lost on September 11, 2001, and February 26, 1993, the 6.5-acre memorial will span three levels below ground and provide access to the original twin towers’ foundations. In this and other ways, the designers set out to create a powerful experience that will remove visitors -- physically and emotionally -- from the city and everyday life.

“The design strives to make visible what is absent,” Michael Arad said. “The primary responsibility we have is to those we lost that day.”

View an animation and a slide show of the latest renderings of “Reflecting Absence."

At street level, memorial visitors will be greeted by a public plaza filled with hundred of trees. The urban forest will stretch across one and a half acres and have at its center two large voids -- cascading pools sunken thirty feet into the footprints of the twin towers -- that will serve as open and visible reminders of the absence of those lost.

Descending from the plaza level, visitors will make their way down two switchback ramps, each as long as a city block, that will take them 30 feet below grade into a central hall. Here, the names of the victims from both terrorist attacks will be inscribed on low parapets encircling each pool. “Memorial Hall,” filling the space between the reflecting pools, will be a vast gathering place where visitors can sit and reflect and events can be held.

Descending further still down to bedrock, visitors will be able to touch the rough concrete of the slurry wall that held back the Hudson River on 9/11. The box-beam columns that supported the towers also will be exposed. Here, at the lowest depth of the site, a room will be set aside for quiet contemplation. At its center, a mausoleum called “Memorial Center,” will house unidentified victims’ remains. A private room, too, will be reserved as a space for victims’ families to gather and share their memories.

As they ascend back to ground level, memorial visitors will be able to view the relocated Vesey Street stairway -- also called the “survivors’ stairway” -- which is one of the only and largest remnants from the original World Trade Center.

To the east of the plaza the 40,000-square-foot, two-story museum pavilion will rise. Designed by international architecture firm Snøhetta the pavilion will serve as the primary entry to the underground memorial. It will be home to WTC relics -- including a pair of the twin towers’ façade’s ‘tridents’ -- and exhibitions about the 1993 and 2001 attacks. Also inside the pavilion will be a 160-person auditorium, café, rest areas, ticketing, security screening, and a private room for use by family members of 9/11 victims.

The Memorial is expected to be partially open by September 11, 2011, and fully complete by mid-2013.

Click here to view the latest animation of "Reflecting Absence."

Click here to see the latest information on Memorial and Museum construction.

Renderings and animations by DBox, courtesy of the Lower Manhattan Development Corporation.