The Pyramid of Menkaure on the Giza Plateau may have a previously unknown entrance.

Two voids found on the eastern face of Menkaure's pyramid may indicate the presence of a second entrance.

Two voids detected on the eastern side of the Pyramid of Menkaure on Egypt's Giza plateau hint at a second, hidden entrance to the pyramid, according to a new study.

The pyramid was built during the reign of the pharaoh Menkaure (circa 2490 to 2472 B.C.). It's the last and smallest of the three pyramids built on the Giza plateau and originally stood about 213 feet (65 meters) tall. The main entrance to the pyramid is located on the northern face.

The eastern side of the pyramid contains an area of polished blocks that have long puzzled researchers. "The stones are remarkably polished over an area around four meters [13 feet] high and six meters [20 feet] wide," the researchers who made the new discovery said in a statement. "Such smooth stones are otherwise only found at what is currently the only entrance to the pyramid, on the north side."

In other words, it's curious that the pyramid has polished stones but apparently no door on its eastern side.

In 2019, independent scholar Stijn van den Hoven published an article on Academia.edu and YouTube suggesting that another entrance to the Menkaure pyramid may be behind the polished blocks. The team decided to test van den Hoven's hypothesis, and over the past three years, the team has been conducting electrical resistivity testing (which measures how much resistance there is to electrical currents), ground-enetrating radar (which uses radio waves to examine what is underneath) and ultrasonic testing (which uses sound waves to examine a structure) on the eastern face of the pyramid.

By combining data from these three methods the team was able to get an idea of what was behind the eastern face of the pyramids. They detected two voids, located close together, with one being about 4.6 feet (1.4 m) behind the eastern face, while the other is about 3.7 feet (1.13 m) behind it, the team said in the statement.

While the findings support the possibility of a second entrance, more tests should be done to gather more data on the anomalies, the researchers wrote in their findings, published in the October issue of the journal NDT & E International.

Peter Der Manuelian, an Egyptology professor at Harvard University who was not involved with the research, said in an email that "this is a very interesting discovery, and shows we still have more to learn about the Pyramids at Giza."

He noted that, with a few exceptions, the entrances to Old Kingdom (circa 2649 to 2150 B.C.) pyramids are on the northern face. "Further exploration will hopefully tell us more about the significance of these voids, whether they are a construction anomaly, part of a second entrance, or something else," Der Manuelian added.

The research was done by a team from Cairo University and the Technical University of Munich as part of the Scan Pyramids project, which has been conducting remote sensing of Egypt's pyramids to learn more about them. Another scientific team with the Scan Pyramids project has been conducting tests on the Great Pyramid at Giza and has found two areas with voids.