The 9/11 Memorial outside the Pentagon, which consists of benches representing each life lost there that day interspersed with trees.
There will be three memorials remembering the lives lost on 9/11: at the site of the World Trade Center in New York; at the Pentagon in Northern Virginia; and at the crash site of United Flight 93 in Shanksville, Pa.
Jeff Reinbold, manager of the Pennsylvania memorial, says everyone struggled with how to commemorate the lives lost in the attacks.
"We asked ourselves the same questions that were being asked in new York and Washington and around the country: how do you even begin to think about creating a memorial in such a short time after the event?" asks Reinbold. "How can you create a memorial that is relevant in 10, 20 years?
The answer for rural Pennsylvania is a 2,000-acre landscape memorial.
But in New York, as museum director Alice Greenwald explains, the memorial has a dual purpose: to honor the victims and educate its visitors.
"It will be at once an archeological site, a story-telling museum, and a memorial institution," says Greenwald.
The memorials in Shanksville and New York will open for the first time on Sept. 11 of this year, while the Pentagon Memorial was completed in 2008.
All three memorials are different, with unique designs and messages, but all were constructed, as one of the panelists put it, "in places of violence and death" which have been transformed into "sacred ground."