Few buildings are still making headlines 4,500 years after their completion. But then, few buildings have been constructed with the vaulting ambition of the Great Pyramid of Giza, Egypt.
Built on the orders of the Egyptian pharaoh Khufu, the 146m-high edifice was the tallest building on Earth for 3,800 years. The only surviving Wonder of the Ancient World, it remains the largest and most enigmatic ancient structure in existence.
And one mystery has lost none of its grip over the millennia: how was it built?
Now a team of archaeologists claim to have found an important clue in the form of a ramp in a quarry.
The idea that ramps were used to get the estimated 2.3 million stone blocks, each weighing around 2.5 tonnes, into position is not new. It’s the fact that the ramp in the quarry has a series of steps and post-holes to either side.
The Anglo-French team claims these would have allowed the blocks to be hauled up by workers on either side using a pulley system – giving them much greater power than simply hauling it behind them.
Tellingly, the ramp is considerably steeper than those previously thought practicable. Furthermore, both the quarry and the ramp were in use around the time of the Great Pyramid, suggesting its builders had access to the technology.
The team, from the University of Liverpool and the French Institute for Oriental Archaeology, Cairo, are planning to report their discovery in an academic journal.
But already some academics are playing down its significance, pointing out there’s no evidence the ramp system was used on the pyramid itself – or that it would have helped much in any case.
The problem is that the huge pyramid is, well, huge and pyramid-shaped. That creates two key challenges: building a system of ramps able to cope with the shape, and positioning each block precisely once off the ramp.
On so vast an edifice, even tiny errors accumulate – creating all kinds of problems on the way up to the apex.
In truth, while attention so often focuses on the sheer effort of shifting the blocks, it’s the precision engineering which really beggars belief.
Each of the four sides of the Great Pyramid’s base is just over 230 metres long, give or take just 59mm, and they are aligned to the four points of the compass to within 0.07 of a degree. The base of the pyramid is also level to within plus or minus 15mm.
Small wonder that, back in the 1970s, a best-selling book claimed the Great Pyramid had been built with help from extra-terrestrials.
Research suggests the Ancient Egyptians needed no such help. It’s likely the pharaoh’s surveyors knew they could create a dead-flat reference level just by creating a water-filled trench.
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Experiments have also shown that simple techniques like counting the rotations of a wheel as it rolls across precisely levelled ground can mark out distances with impressive accuracy.
The real mystery is how such accuracy was maintained on the building itself. Surveys have revealed that the joints between each of those huge block are typically less than a millimetre wide.
One possibility is that instead of being heaved into position, at least some of the blocks were made on the spot. Chemical analysis suggests some are made from an ancient form of cast concrete.
But that still leaves unanswered the mystery of how granite beams – some weighing over 70 tonnes – were shaped and fitted into the structure with such precision.
One thing archaeologists do agree on is that the Great Pyramid was not the work of an army of slaves. Simply put, there was no way to control so many unwilling workers. More likely, most of those on site were skilled craftsmen and labourers.
And perhaps that solves the mystery of how the Great Pyramid was built. It was done by those most prized assets of any worker: ingenuity and pride in the job.
Robert Matthews is Visiting Professor of Science at Aston University, Birmingham
