To honor those who were killed in the terrorist attacks on September 11, 2001, as well as the February 26, 1993, attack, the LMDC held a competition for the design of a memorial at the World Trade Center site. In January 2004, the scheme Reflecting Absence by architect Michael Arad and landscape architect Peter Walker was selected. Davis Brody Bond was selected as the associate architect to execute the design of the memorial in April 2004 and was later commissioned as design architect for the memorial museum in December 2004.

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 National September 11 Memorial & Museum will feature three levels descending below ground and will provide access to the original foundation of the twin towers. 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."

At street level, visitors to the memorial will be greeted by a plaza filled with hundreds of oak trees, intended to create a contemplative space separate from the sights and sounds of the surrounding city. The above-ground forest will stretch across one and a half acres and have at its center two large voids - cascading pools sunken 30 feet into the footprints of the twin towers - that will serve as open and visible reminders of the absence of those lost.

The entrance to the museum will be located on the memorial plaza. Visitors will descend to an orientation area and then farther down to the first main exhibition level. An extensive collection of artifacts, ranging from salvaged building elements of monumental size to modest personal mementos, will be included in the museum exhibits. At this level, the precise spot where a truck bomb was detonated in 1993 is marked. Here, visitors will be able to decide whether to bypass the most sensitive exhibits or not. The final level of the museum will reach nearly to bedrock, between the footprints of the two towers.

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 ground into a central memorial 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 offer a vast gathering place where visitors can sit and reflect and events can be held.

As visitors descend below the memorial voids, they will reach bedrock, where they can touch the jagged steel and rough concrete of the 70-foot slurry wall that held back the Hudson River during the attacks as well as other remaining structures at the foundation of the site. Here, at the bottom-most level of the site, a room will be set aside for quiet contemplation. At its center, a mausoleum, to be called Memorial Center, will house the unidentified remains of victims gathered in the aftermath of 9/11. A private room, too, will exist at bedrock level, reserved as a space for victims' families to gather and share their memories. A visit to the memorial will conclude in the ascent back to ground level.

The design and construction of the National September 11 Memorial & Museum will be one of the most significant undertakings in the history of New York City and a focal point for the revitalization of Lower Manhattan.