A hidden corridor was found recently inside the Great Pyramid of Giza in Egypt, thanks to researchers’ year-long effort.

“An international research team used an imaging method based on cosmic rays to analyze a cavity behind the pyramid’s north face that was first discovered in 2016,” NBC News reported, adding that the team announced its findings, alongside Egyptian officials, on Thursday near the pyramid.

Officials noted the space is approximately two meters wide, and nine meters long. The builders, who erected the royal burial chambers in 2560 BC, may have designed it to relieve the structure’s weight.

An image shows the interior of the chamber, and the crowd gathered for the recent news conference:

Secretary General of the country’s Supreme Council of Antiquities Mostafa Waziri explained the corridor was “protecting or reducing the pressure on something beneath it.”

However, it could be something else, but researchers were working to determine its purpose.

Pharaoh Khufu, who reigned from 2509 until 2483 B.C., built the pyramid on the Giza plateau. He was also known by the Greek name Cheops, and was the second pharaoh of the Fourth Dynasty, according to the BBC:

He was the son of Sneferu and Queen Hetepheres I, and is believed to have had three wives. He is famous for building the Great Pyramid at Giza, one of the seven wonders of the world, but apart from this, we know very little about him.

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Khufu came to the throne, probably during his twenties, and at once began work on his pyramid. The entire project took about 23 years to complete, during which time 2,300,000 building blocks, weighing an average of 2.5 tons each, were moved. His nephew Hemiunu was appointed head of construction for the Great Pyramid. Khufu was the first pharaoh to build a pyramid at Giza. The sheer scale of this monument stands as testament to his skills in commanding the material and human resources of his country.

During the recent press conference, Egypt’s former Minister of Antiquities Zahi Hawass, told reporters, “This discovery, in my opinion, is the most important discovery of the 21st century.”

Video footage shows the vaulted ceiling inside the chamber:

The discovery is thanks to Egypt’s Ministry of Antiquities’ ScanPyramids project that began in 2015. Team members work to look inside the structures, however they do not use drilling methods while they work.

“Instead, scientists used ‘non-invasive and non-destructive surveying techniques’ called muons radiography, developed in Japan by Nagoya University and the High Energy Accelerator Research Organization,” the NBC report stated.

Video recorded at the news conference shows the chamber in the background, with people lined up to get a closer look:

Hawass said news conference was held to tell the world that “technology can reveal lots of secrets. And today, major important secrets have been revealed by technology for the first time,” he explained to the crowd, adding it will uncover facts about Khufu and his pyramids.