The Egyptian pyramids, represented most famously by the pyramids at Giza, are perhaps the most enduring and iconic vestige of the ancient Egyptian civilization. How the pyramids were built, however, remains a source of intense speculation among historians, archaeologists and engineers.
The scale and precision of the pyramids demonstrate the Egyptians’ extraordinary skills in mathematics, astronomy, logistics and advanced engineering. Unfortunately, the Egyptians did not devote the same level of effort to documenting their planning and construction processes. Much of what we know about how the pyramids were built, therefore, comes from observations made and artifacts unearthed by archaeologists at Giza and other Egyptian pyramid sites.
Lessons From History
To understand how the pyramids were built is to understand the history of engineering in the Old Kingdom of Egypt, a period spanning 2575 to 2134 B.C.
The three major pyramids at Giza were designed and built to serve as tombs, respectively, for Egyptian pharaohs Khufu, his son Khafre, and Khufu’s grandson, Menkaure, between 2540-2460 BC, explains engineer Craig B. Smith in his book “How the Great Pyramid Was Built.” These structures represent the pinnacle of Egyptian pyramid building, but their stature as engineering wonders is built on a foundation of lessons learned from the construction of earlier, less famous pyramids.
One of the earliest Egyptian pyramids, for example, is the Step Pyramid begun by Pharaoh Djoser in 2620 B.C. at Saqqara. Its series of stepped, concentric platforms represented the first significant architectural departure from early Egyptian tombs, which featured flat, slightly raised platforms known as mastabas, according to Smith.
Another major step forward in the history of engineering came with the pyramid at Meidum begun by Pharaoh Sneferu in 2570 B.C., Smith details. It was the first pyramid to incorporate corbelled ceilings in underground chambers, an approach that afforded elegant, arched ceilings. Unfortunately, this pyramid, like the Step Pyramid, achieved its sloping exterior shape with courses of inwardly leaning stones, an engineering approach that would prove untenable.
A More Level Approach
The Bent Pyramid, begun by Pharaoh Sneferu in Dahshur in 2565 B.C., added several critical chapters to the history of engineering, Smith recounts. Its site consisted of loose, sandy soil, a foundation that provided inadequate support for the heavy structure. Predictably, the pyramid began to sink as construction proceeded, a result of using inwardly leaning blocks on an unstable foundation. To reduce stress on the structure, the pyramid’s architects and builders reduced the slope of its exterior sides by 10 degrees, which created a “bent” appearance for the upper two-thirds of the structure.
Serendipitously, this structural resolution produced the most significant breakthrough in how the pyramids were built: New courses of blocks (for this and all future pyramids) would be laid horizontally to reduce stress on the pyramid’s inner core. And the pyramids’ smooth, angled sides would be achieved using horizontal courses of stone finished with angled faces.
Rules to Build By
The Red Pyramid, begun in 2560 B.C. by Pharaoh Sneferu, marked the zenith of engineering lessons learned. It would serve as a prototype for the Great Pyramid, the first pyramid at Giza. It also codified the following lessons for pyramid building, as laid out by Smith:
- Build the pyramid on solid rock to ensure adequate support for its structure.
- Use precise measurements (square, plumb) to maintain the pyramid’s shape.
- Place the burial chamber within the pyramid, not in the ground under the pyramid.
- Place masonry courses horizontally to better distribute the loads.
- Use large blocks on the lowest levels to create an accurate and stable base. Use smaller blocks on higher levels as they will be easier to place.
- Use corbelled ceilings to create spacious, dramatic rooms, while providing the structural strength required.
- Select a pyramid angle that minimizes labor and maximizes height.
- Finish the pyramid with fine white limestone to make it visible from great distances.
The most remarkable aspect of the Egyptians’ success building pyramids is the absence of any sophisticated mechanical tools. They had no wheels or pulleys for moving or lifting loads, and no iron tools. Instead, they relied on copper chisels and drills, rudimentary copper saws and smooth, round balls of dolerite, a hard stone, to cut limestone, according to Smith.
But what the Egyptians lacked in tools, they made up for with science and engineering precision.
Smith explains that they developed and used the cubit rod to measure and lay out the dimensions of the pyramid; a square level to level horizontal surfaces, and a 3:4:5 framing square to create precision 90-degree angles.
And the work paid off. The pyramids at Giza are oriented nearly precisely north and south. And the southeast corners of the pyramids are aligned on a diagonal that runs almost exactly 43 degrees east of true north, despite the fact that the compass had not yet been invented, according to Smith.
Tools of the Trade
Evidence uncovered by archaeologists such as Mark Lehner, director and president of Ancient Egypt Research Associates, suggests that most of the stone used in the pyramids came from quarries close to Giza, in his book “The Complete Pyramids.” His findings also indicate that the white, homogeneous limestone used to provide the pyramids’ finished outer layer was brought to Giza by boat from quarries east of the Nile, and that granite, the other major type of non-local stone, was brought from Aswan.
The Egyptians cut limestone from the quarries by first chiseling out a slot along three sides of a block, drilling holes along the bottom edge, then using levers inserted in these holes to break the block loose from the quarry wall, Smith notes.
Blocks of stone could be “tumbled” short distances using wooden sticks like levers. More often, the blocks were levered onto wooden sledges and hauled by teams of labors across “roads” fashioned in beds of limestone chips and mortar interlaced with wooden beams. Wet, alluvial mud or wooden “rollers” placed under the sledge runners likely allowed laborers to move the sledges more easily, according to Lehner.
Archaeologists also believe that once the stones were on site, the Egyptians used inclined ramps to move them up to higher levels of the pyramid. A key debate, however, focuses on the configuration of these ramps: were they straight-on, perpendicular, spiral or perhaps zig-zag ramps built on the pyramid or just leaning against it? Whatever their design, these ramps had to bring stones to the right level while allowing pyramid builders to verify, visually, that the structure was maintaining its desired shape, Lehner explains.
A National Legacy
The Egyptian pyramids, one of the last remaining Seven Wonders of the World, remain a fascinating and extraordinary chapter in the history of engineering. They are a testament to human organizational skills, the extraordinary vision of the ancient Egyptians and the sheer determination of a civilization to succeed.
Some naysayers and historians have suggested that projects the size of the Egyptian pyramids could only have been executed by aliens. Archaeologists, like Lehner, however, are confident that these remarkable structures are the result of human hands performing work in small increments repeated innumerable times.
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