It's the ultimate riddle of the sphinx that has vexed scholars for centuries: just why did the Ancient Egyptians stop building the pyramids?
And now, some 4,500 years after they were made, an intrepid Welsh structural engineer may just have stumbled upon the answer.
Newport-based businessman Peter James has spent months in Egypt examining how the famed structures began to fall apart.
The long-held explanation is that looters picked away at the massive stonework over the years.
But unconvinced by the idea, Mr James – dubbed “Indiana James” by his team in homage to Hollywood’s all-action archaeologist – came up with a new theory that points to nature and physics as the primary culprits.
He suggests “thermal movement” contributed to the decision to stop using the pyramids.
The former Royal Navy lieutenant-commander and founder of global engineering firm Cintec came to his conclusion after being asked to examine the “outer cladding” of the wonderfully-named King Snefru’s Bent Pyramid, outside Cairo.
He believes the pyramids were constructed so precisely they weren’t able to deal with the contraction and expansion of the limestone in the desert heat, and that ironically, the most crudely built one — the Bent Pyramid — has held up best through time.
The Bent Pyramid, which got its name because of its awkwardly bent top, was built by Snefru (the first Pharaoh of Ancient Egypt's 4th dynasty) in around 2600 BC
There is major damage to its surface – the smooth limestone cladding has partly disappeared.
“I looked at it from a builder’s point of view, not that of an archaeologist,” he said.
“It was obvious we needed to find the mechanism of failure.”
Some had suggested thieves pillaged the stones – a theory which James says seems highly dangerous, labour intensive and unlikely.
“The Bent Pyramid is one of the oldest is the only one with any degree of stone casing still attached, making the mechanism of failure apparent,” he said.
“The temperatures in the Egyptian desert fluctuate so dramatically, from day to night that the pyramid’s blocks expand and contract, ultimately cracking and falling apart.
“During the day, the temperature rises to 400C across the face of the outer casing, then at night cools to 30C because of the lack of cover and exposure to the prevailing winds. This gives an average daily temperature fluctuation of 370C. Imagine that happening day in day out for thousands of years.
“Photographs of the Bent Pyramid show how thermal expansion has caused the blocks to shift to the edges, where they have detached. It also shows how individual stones, unsupported, can cantilever and snap off and subsequently fall to the ground.”
Mr James said as Egyptian construction methods became more sophisticated, spaces between the stone would have become tighter, giving less room for movement and increasing the probability of damage.
The former Cardiff council buildings inspector has worked on everything from England’s Windsor Castle and Buckingham Palace, to the White House, Jerusalem’s sacred Wailing Wall and Egypt’s Red and Step Pyramids.
Expanding on his theory, he added: “The Bent Pyramid was one of the first ever, at a time when building skills were not as well honed. It begged the question why did it still have its outer casing attached, while the Red Pyramid and the Great Pyramids at Giza have virtually none?
“I believe that this is due to the increased skills of the craftsmen, who developed more knowledge and precision as the process of pyramid construction developed. They became able to provide better accuracy, build quality, and jointing of the slabs. The Bent Pyramid was probably built with less precision and with more voids between the stones that acted like expansion joints. The casing blocks being inclined inwards at the base of the pyramid may have limited the expansion.”
James believes the sight of the progressive damage to the outer edges of the pyramids – that would have taken place relatively soon after their construction – is a credible reason the Egyptians changing their burial methods.
“Imagine spending 25 years of constructing these wonderful monuments, only to see them cracking around their edges.
“It is far more credible that the cladding cracked off and was subsequently stolen, rather than thieves risking their lives to shift three-tonne stones.”