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.
Oli Scarff/Getty Images
CNN, CNC3, Facebook, WPLG, FIFA TV
JIM WATSON/AFP/Getty Images
Marc Longoria/CNN iReport
Philipp Schmidli/Getty Images
Selcuk Acar/Anadolu Agency/Getty Images
Spencer Platt/Getty Images
Sign up for Breaking News, Daily Headlines, Severe Weather Alerts & more!