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.

The artifacts found with mummies date back the era that started with Alexander the Great's conquest of Egypt. They were the first human mummies discovered in the area, a site rich in artifacts which lies near the Nile Valley city of Minya.

The eight-meter (9-yard) deep necropolis included six sarcophagi, two clay coffins, two papyri written in demotic script and several vessels. The mummies were elaborately preserved and were likely officials and priests.

At the edge of the necropolis, legs and feet of other mummies could be seen, pointing to a much bigger find. Excavation is still at the preliminary stage.

Egypt's economically-vital tourism industry has largely collapsed since the 2011 uprising against longtime dictator Hosny Mubarak. The Ministry of Antiquities said the latest finds were "as if our ancestors are sending a message for tourism to come back strongly."

The discovery comes after a series of important finds in Egypt. Eight mummies were uncovered inside a 3,500-year-old tomb in the southern city of Luxor in April. A month earlier, a massive colossus likely depicting the 26th dynasty King Psamtik I was unearthed in Cairo.

Salah al-Kholi, a Cairo University professor of Egyptology who headed the expedition, said his team found burial shafts and that excavation work "revealed that these shafts led to a number of corridors inside a cachette of mummies."

Kholi said the discovery was "the first human necropolis found in central Egypt with so many mummies." There could be as many as 32 mummies in the chamber, including mummies of women, children and infants.