The tallest and oldest of the three large pyramids on the Giza Plateau has a mystery sealed inside.
More than 4,500 years after it was constructed to house the remains of Pharoah Khufu, a team of more than three dozen researchers announced Thursday that they’ve discovered a huge, secret space hidden behind its walls, according to a report in Nature.
The massive void is located above what’s called the Grand Gallery — a passage with 28-foot ceilings that leads to Khufu’s tomb — and measures at least 100 feet in length.
While Khufu’s pyramid, often times called the Great Pyramid, is one of the seven wonders of the world, it’s mostly remained shrouded in mystery. There’s no other structure quite like it and it’s status as a national heirloom makes it difficult to probe.
Great Pyramid of Giza
Great Pyramid of Giza
Amazing Scene for Giza Pyramids
The Great Pyamid of Giza at the Giza plato, Egypt on January 1, 2010. (Photo by Ramin Talaie/Corbis via Getty Images)
The sun sets over houses, minarets and the Great Pyramids of Giza (R) during a cold and wet day in the Egyptian capital, Cairo, Egypt, January 27, 2016. Picture taken January 27, 2016. REUTERS/Amr Abdallah Dalsh
THE GREAT PYRAMIDS OF GIZA - JANUARY 3, 2017: DigitalGlobe satellite imagery of the Giza Pyramid Complex on the outskirts of Cairo, Egypt. Photo DigitalGlobe via Getty Images.
A group of camels and horses stand idle in front of the Great Pyramids awaiting tourists in Giza, Egypt, March 29, 2017. REUTERS/Mohamed Abd El Ghany
A man waits for tourists to rent his camel in front of the Great Giza pyramids on the outskirts of Cairo, Egypt, August 31, 2016. Picture taken August 31, 2016. REUTERS/Mohamed Abd El Ghany
Cairo, Egypt the Great Sphinx of Giza standing tall with the Great Pyramids of Giza in the background. This particular one is The Pyramid of Khafre, the second largest of the three great pyramids.
Cairo / Egypt
Pyramid of Khafre and old monuments at Giza plateau.
Egypt, Cairo: dromedary in front of the Great Sphinx and the Great Pyramid of Giza (also known as the Pyramid of Khufu or the Pyramid of Cheops) on the Giza Plateau. (Photo by: Andia/UIG via Getty Images)
CAIRO, EGYPT - JUNE 28: ï¿½A horse stands in a stable near the Great Pyramids of Giza on June 28, 2012, in Cairo, Egypt. In one of his first public policy statements since election results were released, Egyptian President-elect Mohammed Morsi said reviving Egypt's troubled tourism industry will be a major priority during his first 100 days in office, as part of a major push to strengthen Egypt's ailing post-revolution economy. Morsi's campaign told local media on Thursday that Egypt's tourism industry could not achieve new growth without stability and an atmosphere that encouraged foreign tourists to visit Egypt. Tourism forms more than 10% of Egypt's economy and employs an estimated one in eight Egyptians. (Photo by Ed Giles/Getty Images)
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A team of experts at ScanPyramids, however, realized the technology used to examine the insides of a volcano — called muography — could be used to look within the pyramids. The technology relies on high-energy cosmic rays, which shoot subatomic particles called muons toward the ground.
Muons are slowed by large masses, like the rocks used to make up the pyramids. By placing muon detectors in strategic areas, researchers are able to track the particles moving through space. They rely on them to create a sort of picture, which reveals whether an object is made up of a dense material or is a completely empty space.
“This void was hiddien in the construction of the pyramid. It is not accessible and we needed this new technique, at the right time, to identify and to discover it,” Mehdi Tayoubi, a co-founder of the HIP Institute and a researcher with ScanPyrmids, told reporters.
Still, no one yet knows what the passage is exactly.
Mark Lehner and Zahi Hawass, members of the Egyptian Ministry of Antiquiteis’ scientific committee — both of whom saw the findings — told The Atlantic they suspect it is a “construction gap.”