On Friday afternoon, reports came in that there had been a fire at the Flight 93 memorial in Shanksville, Pennsylvania. The fire destroyed the headquarters and superintendent’s office at the memorial, which is of course in place to honor the crash site of one of the hijacked planes from September 11, 2001.

According to a report from WXPI.com, a Pittsburgh area news source, the fire destroyed numerous irreplaceable memorial items, including the flag that was flown over the United States Capitol building on 9/11. Also lost were several personal items from passengers who lost their lives aboard Flight 93. Some of these items were recovered from the crash site, while others were donated to the memorial by friends and family members of the late passengers.

The list of items burned by the fires goes on and on, encompassing at least 100 “tribute items” that had been left at the memorial site in the 13 years since that tragic day. DVDs of various meetings and memorial services held each year by the Flight 93 National Memorial Federal Advisory Commission were also lost in the fire.

Luckily, the DVDs were merely copies and should be able to recreated. 100 tribute items is also just a small percentage of the mementos that have been left at the memorial site over the years. The WXPI.com reports claims that nearly 60,000 tribute items have been collected since the memorial was first established. Most of them are stored offsite. Also preserved were the oral histories and photo archives of Flight 93 and its passengers.

As of yet, there has been no concrete explanation given for the fire. The National Park Service and the Pennsylvania State Police are both in the process of investigating the fire, in hopes of determining the cause.