The pyramids: mysterious graves of the ancient Egyptians

In 2015, French researchers detected a possible void above a descending corridor. But after several instances in recent years of supposedly newly-discovered pyramid chambers that remained unproven, the researchers sought to back the clue up with quantifiable proof. Now it's official: there is indeed a gap within the structure. But is it a chamber?

In May 2016, scientists set up a device in front of the Cheops Pyramid that can register muon particles, a byproduct of cosmic radiation. Measurements revealed a void at least 30 meters in length (99 feet) within the largest pyramid at Giza.

The French and Japanese scientists installed detectors in the Cheops Pyramid's interior passageways as well. Muon particles function like x-rays in a human body but can penetrate hundreds of meters of rock. A small portion are deflected — and the differing quantities of particles passing through the stone allow researchers to draw conclusions about wall thickness.

Located on the west bank of the Nile at the edge of the Egyptian desert about 20 kilometers (13 miles) from Cairo's city center, these pyramids are the last surviving ancient wonders of the world — and the largest made by man. They are among the best known and oldest structures of humanity, dating back over 4,500 years.

This photo of the sphinx in front of the Cheops Pyramid was made in 1963 before it had been declared a UNESCO World Heritage Site. That happened in 1979, when the Cheops Pyramid and many others were inducted as part of the complex titled "Memphis and its City of the Dead — the Pyramid Fields from Giza to Dahshur."

Back in 1335, a monk from Lower Saxony named Otto von Nienhusen visited the pyramids of Giza and was able to view the interior of the Cheops Pyramid. In the late 18th century, British and German archaeologists began exploring it. Now there's fresh hope that new scientific methods can reveal tunnels and perhaps even grave chambers.