The Great Pyramid of Giza - an Engineering Enigma
Since its construction 4,500 years ago, the Great Pyramid of Giza, the only standing one of the seven wonders of the ancient world, has remained an engineering enigma.
How this ancient manmade structure was built? We know that after the completion of the step pyramid of Djoser in Saqqara, succeeding pharaohs wanted to be buried or remembered eternally by such types of monuments. But it wasn't until pharaoh Khufu (about 2547-2524 B.C.) built his pyramid with the help of his architect brother Hemienu ("overseer of all construction projects of the king") that pyramid building came to perfection.
There are close to seventy pyramids of various sizes scattered around the outskirts of present day Cairo. Snefru (father of Khufu) alone had attempted in his lifetime several pyramids which today still stand in the Memphis-Dashur area. Though not often visited by tourists, these structures are revealing of the different approaches and construction techniques employed by ancient Egyptian builders to create so many of these massive structures without iron tools, pulleys or wheels.
From the study of these monuments, scholars assume that most pyramids consist of a solid core similar to a crude step pyramid, to which masons added packing stone to smooth out the slope and then an outer casing of limestone or granite to create the perfect pyramid shape. However, an ancient Egyptian pyramid was a structure meant to be used, and thus it had to have an entrance, interior passages and chambers, as well as the so called ventilation shafts, which, according to some, were precisely angled to specific points in the night sky - all carefully thought out ahead of construction.
The major problem that all pyramid builders had to face was getting the large stone blocks to the height they required, for which it is generally understood that ramps were employed. But before we get into the theories regarding how these ramps were actually designed and used, lets review what entails the successful creation of a pyramid the size of Khufu's; the mighty tasks it involves and the huge difficulties to overcome.
The design: The perfect pyramid consists of a square base with four isosceles triangles with their top vertices meeting exactly at the center of the square as seen from the top. The inclination of the sides of the pyramid is highly significant for both the aesthetic beauty and stability in its construction. The Bent Pyramid of Snefru had its angle of inclination severely reduced halfway in the project to prevent its inevitable collapse.
The measurements: Precisely crafted surveying instruments and ingenious techniques are needed to come up with the exact measurements required to have the top vertices of a pyramid of huge dimensions meet dead center. Egyptian architects, surveyors and builders are known to have used two specialized surveying tools, the merkhet (the 'instrument of knowing', similar to an astrolabe) and the bay (a sighting tool probably made from the central rib of a palm leaf). These allowed construction workers to lay out straight lines and right-angles, and also to orient the sides and corners of structures, in accordance with astronomical alignments.
The terrain: Archaeologist Flinders Petrie suggested that the Egyptians cut a grid of shallow trenches into the bedrock, flooded them with water and leveled the area of construction to a perfect horizontal accordingly.
Resources: The project requires millions of blocks of heavyweight quarried limestone transported to the work area, cut and hauled by thousands of workers using the simplest human or animal traction machinery for transportation and masonry under the supervision and sustenance of the state.
Timeframe: The pyramid must be finished hopefully before the pharaoh dies. That explains why the Great Pyramid of Khufu has three burial chambers, the first built underground, the second (so called Queen's Chamber) some meters above the surface and the third (the King's Chamber) in the center of the structure. Hemienu had to make sure that a burial chamber already existed in case the pyramid was in an unfinished state when it was supposed to be used.
Previous theories have suggested that the Great Pyramid builders raised the man made structure’s millions of stone blocks using an external ramp, either extended, or spiral.
The main difficulty in the single external ramp theory is that the structure required to haul the blocks effortlessly to the top of the Great Pyramid (nearly 480 feet above the ground) would need a slope of a maximum of 8 degrees, which implies a mile long ramp with a volume as large as the pyramid itself, effectively doubling the labor for a structure meant to be dismantled after the pyramid is complete.
A more sensible hypothesis is that of a ramp spiraling upwards around the Great Pyramid as each block is put into place. This approach does away with the need for a massive single ramp. The main objection to the external spiral ramp theory is that such a structure prevents the completion of corners until the pyramid has been assembled. Frequent and precise measurements of the angles at the corners of the pyramid are needed to assure that the four triangular sides would meet at the top. Another objection is the likelihood of collapse by dragging heavy stone blocks on a ramp not firmly fixed to the structure. -No evidence of fixing points have been found on the outside of the Great Pyramid.
As recently as 2007, French architect Jean-Pierre Houdin proposed that the most effective way for the ancient Egyptians to build the Great Pyramid at Giza is the use of an internal ramp that, according to the architect and supported by microgravity measurements conducted in 1986, still exists inside the ancient manmade structure. In his computer model, Houdin's ramp never interferes with the passageways leading to the burial chambers and the Grand Gallery, adding credibility to his theory. The first stage of construction, according to Houdin, used a traditional external ramp that led up to a height of 43 metres (140 feet) from the base. Once completed, this volume of material would account for more than 70 per cent of the pyramid's total mass.
The next stage involved building the internal ramp in the shape of a spiral. "It was like a tunnel with a covered roof, but open to the sky at the four corners of the pyramid so that the stone blocks could be turned," M. Houdin said. Once the bulk of the pyramid was finished, the open corners of the ramp were filled in as the pyramid was finished off, but the ramp's tunnels were left empty. Scientists are now seeking permission from the Egyptian government to do more non-invasive tests that would prove or disprove Houdin's theory.
None of the theories mentioned above is currently supported by solid evidence or ancient documentation. Further investigation needs to be conducted at the Giza plateau itself to finally solve the engineering enigma on how the Great Pyramid of Giza was built.