Look back at some of the work that went into building the memorial to United Flight 93 in Pennsylvania.
Tokens honoring Flight 93 sit near the fence surrounding the permanent memorial's construction site in May 2011.
Henry S. Dziekan III/Getty Images
Library of Congress
Mario Tama/ Getty
National Archives and Records Administration
Mark Davis/Getty Images
iStock / Spauln
WDBJ via Newsource
Barry Williams/Getty Images
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