...as scans suggest they could be a secret entrance

Around 4,500 years after it was constructed, scientists think they've located the remains of a hidden entrance at a historic pyramid in Egypt.

Built around 2510 BC and standing nearly 200 feet tall, Pyramid of Menkaure is the smallest of the three main pyramids of the famous Giza complex. 

It was built to serve as the tomb of the King Menkaure, the Fourth Dynasty king whose sarcophagus mysteriously went missing.  

Researchers in Egypt and Germany have used high-tech scanning methods to peer behind the pyramid's historic granite bricks. 

They report that there are two hidden air-filled anomalies which suggest a hidden entrance undetected in the modern era until now. 

Christian Grosse, professor of non-destructive testing at Technical University of Munich (TUM), called it 'an important finding in Giza'. 

'The testing methodology we developed allows very precise conclusions to be drawn about the nature of the pyramid's interior,' he said.  

'The hypothesis of another entrance is very plausible, and our results take us a big step closer to confirming it.'  

Around 4,500 years after it was constructed, scientists think they've located the remains of a hidden entrance at a historic pyramid in Egypt.

Pyramid of Menkaure, - the smallest of the three main pyramids of the Giza pyramid complex, standing at nearly 200 feet tall - had a second entrance, experts think. In this photo, the northern side (featuring the primary entrance) is in shadow. The southern side is illuminated by sunlight. Also seen are three much smaller pyramids known as the Queens' Pyramids

The Menkaure pyramid's primary entrance is on its northern side, but experts think the second one is on the eastern side, which faces the River Nile.

In particular, they point to a 13ft by 19ft (four metres high and six metres wide) rectangular area of the eastern side that's close to the ground. 

Weirdly, the granite blocks in this area of the eastern façade are 'unusually smooth' as if they'd been rigorously polished millennia ago. 

Tellingly, such smooth stones are found at the primary entrance on the northern side – suggesting a second one long existed here too but has been forgotten. 

Independent researcher Stijn van den Hoven theorized this possible additional entrance for the first time in 2019, but this has remained a hypothesis – until now. 

The experts at Cairo University and Technical University of Munich (TUM) used 'non-invasive' methods – radar, ultrasound and electrical resistivity tomography (ERT) – to peer inside without pulling apart the ancient bricks. 

Excitingly, they detected two air-filled voids behind the smooth façade, both of different sizes and at different heights. 

One of the air-filled 'anomalies' is located at a depth of 4.5 feet (1.4 metres), measuring 3.2 feet by 4.8 feet (1 metre high by 1.5 metre wide), while the other anomaly is at a depth of 3.7 feet (1.13 metres), measuring 2.9 feet by 2.2 feet (0.9 metres by 0.7 metres). 

The research using radar, ultrasound and ERT prove the existence of two air-filled voids underneath the eastern façade, providing initial evidence to support the hypothesis

What is the Pyramid of Menkaure?

Pyramid of Menkaure is the smallest of the three main pyramids of the Giza pyramid complex - Khufu, Khafre, and Menkaure. 

Built in around 2510 BC, it currently stands at 200 feet (61 metres) tall with a base of 356 feet (108.5 metres). 

Pyramid of Menkaure is thought to have been built to serve as the tomb of the Fourth Dynasty King Menkaure. 

Why the two void-filled spaces are arranged exactly like this is puzzling, but together they 'could support the hypothesis of a second entrance'. 

The team point out that each technique used in this study has its own limitations, but by using a combination of all three their conclusions are reliable. 

Today, tourists can go inside Pyramid of Menkaure and traverse its burial chambers, corridors and other little niches, but a second entrance on the eastern side hints that there could be still undiscovered chambers or passages containing treasures unseen by modern eyes. 

However, the interpretation of the detected anomalies should be 'discussed among Egyptologists' before any firm conclusions are made. 

Researchers caution it was 'difficult to determine how far the anomalies extend inside the pyramid' due to limitations in the penetration depth of their methods. 

Nevertheless, the study published in NDT & E International, marks the first time structural anomalies have been identified behind the distinctive façade on the east side. 

It's believed Pyramid of Menkaure was built to serve as the tomb of Menkaure, the Fourth Dynasty king, who died as a young man in 2503 BC for reasons unknown. 

Pictured, the location and dimensions of the detected anomalies overlaid on a photograph of the Eastern face of Menkaure

The hypothesis of an entrance is very plausible': Researchers have identified two air-filled voids in the Menkaure Pyramid by using non-invasive methods 

Unfortunately, the sarcophagus within the pyramid was lost at sea nearly 200 years ago during attempts to transport it to the British Museum in London. 

The merchant ship carrying it, Beatrice, was mysteriously lost after leaving port at Malta on October 13, 1838.

The Giza complex, west of Cairo, includes the pyramids of Khufu, Khafre, and Menkaure, along with the Great Sphinx. 

All are shrouded in mystery due to their unclear construction methods, precise astronomical alignment, and still-debated purpose.