How the Egyptian pyramids were built over 4,000 years ago has been one of the great mysteries of the ancient world.
Despite their age, more than 100 of them remain standing today, showcasing just how skilled the Ancient Egyptians were at construction.
The largest, the Great Pyramid of Giza, was originally 147 metres tall and is made up of about 2.3 million stone blocks, each weighing between 2.5 and 15 tonnes.
Each would have had to be transported to the building site and lifted into place using only the techniques available at the time.
This process is equivalent to lifting a double-decker London bus to the top of St Paul’s Cathedral – repeated several million times over.
“There’s still debate between scientists on the exact method of raising these heavy blocks to such great heights,” explained Dr Eman Ghoneim, a professor at the University of North Carolina Wilmington.
However, recent research is helping to uncover the mystery as to how these incredible structures were achieved.
The most widely accepted theory is that ramps were used to haul the stones up – this is supported by remains of inclined structures found close to some of the pyramids. But, the steepness of these ramps has been the subject of debate.
In 2018, Dr Roland Enmarch, a senior lecturer in Egyptology at the University of Liverpool and his team, made a breakthrough by discovering a ramp cut into rock at a quarry at Hatnub, in the Eastern Desert of Egypt, which was an important source of alabaster (soft rock) used in the pyramids.
The angle of the ramp was more extreme than expected, with a slope of more than 20% – previous estimates suggested that ramps in Ancient Egypt wouldn’t have exceeded 10%.
The team was studying inscriptions at the quarry that date back to the time the Great Pyramid was built, suggesting that a similar ramp could have been used in its construction.
Dr Enmarch said: “If you don’t have a very steep ramp, then you need a ramp of such enormous proportions to get to the top of the Great Pyramid that it would be a greater engineering feat than [building] the pyramid itself.”
The process of planning and building a pyramid had to be achieved under strict time constraints.
The average life expectancy in Ancient Egypt was just 35 years, meaning the construction of the pyramid, which would eventually become the pharaoh’s tomb, typically started at the beginning of a reign.
The Great Pyramid of Giza is thought to have been completed in 20 years.
Frank Müller-Römer, an archaeologist at the Institute of Egyptology and Coptology in Munich, Germany, developed a theory of how the pyramids were erected: he is convinced that several ramps, arranged along the outside of the structure, would have been used on all four sides.
He said: “My theory offers a coherent solution for the construction of the pyramids in the shortest possible time.”
How workers and materials were transported to the sites has also been questioned. The Nile River was the main waterway used to carry goods at the time. But although studies have hinted at the presence of ancient branches of the Nile or canals close by, their exact location and size were unclear.
“Over time, the Nile River shifted and branches disappeared because they silted up. There’s still an area in the upper and lower streams that needs to be mapped and this is what we’re after now,” explained Ghonheim.
“We don’t have the complete picture yet.”