Immutable Laws of Friction: Preparing and Fitting Stone Blocks into the Great Pyramid of Giza

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The exact techniques employed by ancient Egyptian craftworkers in the construction of the Great Pyramid of Khufu at Giza during the Fourth Dynasty (c.2649-2513 BC) are still uncertain. Two of the major problems concern the preparation and fitting of the large stone blocks, which were achieved to a high degree of accuracy. A key factor was the friction developed between two surfaces, which controlled the degree of sliding of one stone block over another. Here, data obtained from experiments in measuring the blocks shows how plane surfaces could be prepared which were nearly perfectly flat. Other experiments showed how the blocks could be moved, with the use of lubrication, to lessen the effects of the immutable laws of friction.

Preparing surfaces

The tasks of the mason consist of producing horizontal and vertical surfaces which are precisely flat, and these would require cutting and shaping tools and measuring instruments. Replicated and reconstructed copper, bronze and stone tools for shaping hard and soft stones have been manufactured and tested (Zuber 1956: 180, figures 18-20; Stocks 1986; 1988: 1, 17-99, II, 246-73). The tests indicated that stones of hardness Mohs 3, or below (including soft limestone), could effectively be cut with copper and bronze chisels and adzes. Stones harder than Mohs 3, including even calcite (Egyptian alabaster) had to be worked with different combinations of stone tools--pounders, hammers, picks, axes, chisels, punches, scrapers and sandstone rubbers. In addition to copper tools, stone implements were sometimes employed for shaping and smoothing soft limestone objects (Petrie 1938: 30)

Preparing the surfaces of the Great Pyramid's limestone core- and casing-blocks was a two stage process. The average size of the blocks, according to W.M.F. Petrie (1883: 210, note) is 50 x 50 x 28 inches (1.27 x 1.27 x 0.71m). The bottom surfaces were already flattened and smoothed before inserting them into the structure of the pyramid (Edwards 1986: 283). The blocks' top surfaces were only made truly horizontal, flat and smooth after being fitted into the pyramid (Clarke & Engelbach 1930: 100): this system ensured that any block's top and bottom surfaces were parallel, essential for making each layer of blocks horizontal throughout the pyramid. The four vertical sides of a core-black were only roughly finished (Clarke & Engelbach 1930: 81), and not intended to fit closely to neighbouring blocks. However, abutting end-faces on casing-blocks formed tightly fitting rising-joints.

Ancient masons needed reliable tools for checking that the horizontal joint surfaces of all stone blocks were made accurately flat and truly horizontal, in addition to making flat and parallel the rising-joint surfaces of adjacent casing-blocks. Known instruments for testing horizontal and vertical surfaces all depend upon a hanging plumb line. Such instruments were the frame for testing horizontal planes, shaped like the letter "A", and the vertical testing frame, both made of wood. Models of the horizontal and vertical testing tools were found in the Nineteenth Dynasty (c.1315-1201 BC) tomb of the architect Senedjem at Deir el-Medina, an Upper Egyptian workers' village (Petrie 1917: 42, plate XLVII, B57, 59). The earliest plumb bobs (Petrie 1917: 42, plate XLVIII, B64, 65) date to the Third Dynasty (c.2687-2649 BC).

Calibrating a replica 'A' flame (Stocks 1988: II, 368) required the two bottom ends to touch the surface of still water, while simultaneously marking a vertical line on the horizontal bar exactly behind the hanging plumb line. This tool proved to be as reliable as a modern spirit level (Figure 1). A replica vertical testing tool was also constructed (Stocks 1988: II, 369). Provided the two horizontal pieces of wood were accurately made and fitted to the vertical piece, the tool's reliability also compared favourably with a spirit level (Figure 2). …