Microstructural Evidence of Reconstituted Limestone Blocks in the Great Pyramids of Egypt M. W. Barsoum w and A. Ganguly Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania 19104 G. Hug LEM ONERA-CNRS, Chaˆ tillon Cedex, France How the Great Pyramids of Giza were built has remained an enduring mystery. In the mid-1980s, Davidovits proposed that the pyramids were cast in situ using granular limestone aggre- gate and an alkali alumino-silicate-based binder. Hard evidence for this idea, however, remained elusive. Using primarily scan- ning and transmission electron microscopy, we compared a num- ber of pyramid limestone samples with six different limestone samples from their vicinity. The pyramid samples contained microconstituents (lc’s) with appreciable amounts of Si in com- bination with elements, such as Ca and Mg, in ratios that do not exist in any of the potential limestone sources. The intimate proximity of the lc’s suggests that at some time these elements had been together in a solution. Furthermore, between the nat- ural limestone aggregates, the lc’s with chemistries reminiscent of calcite and dolomite—not known to hydrate in nature—were hydrated. The ubiquity of Si and the presence of submicron sil- ica-based spheres in some of the micrographs strongly suggest that the solution was basic. Transmission electron microscope confirmed that some of these Si-containing lc’s were either amorphous or nanocrystalline, which is consistent with a rela- tively rapid precipitation reaction. The sophistication and endurance of this ancient concrete technology is simply astounding. I. Introduction H OW the Great Pyramids of Egypt were built has been, and remains, an enduring mystery. Attempts to fit the historical and physical evidence into a coherent whole have failed, leading to intemperate speculation. The prevailing model 1–3 is one in which blocks of limestone were cut in local quarries, cut to shape using copper (Cu) tools (bronze came later), transported to the pyramid site, and then hauled up ramps and hoisted in place using wedges and levers. This ‘‘carve and hoist’’ hypothesis, based on accepted models of Egyptian life of the time, has a number of problems, some of which are: (1) Khufu’s pyramid contains some 2.3 million blocks, aver- aging 2.5 tons each, with average dimensions of  1.3 m  1.3 m  0.7 m. Some of these blocks are placed in tiers whose edges closely conform to the pyramidal envelope, although the tiers vary from 0.5 to 1.25 m in thickness with abrupt changes in the thickness of proximate tiers. 1 Precision surveying, masterful management, and expert craftsmanship in forming and place- ment of these massive blocks are implied. And while at first blush the current paradigm appears plaus- ible, on closer inspection the following problems are obvious: (i) quarrying limestone is wasteful, with substantial breakage; yet, waste piles of the expected magnitude are absent. (ii) Cu is soft, so chisels quickly blunt in carving limestone, requiring frequent sharpening, substantial supplies of Cu, slow work, and imperfect surfaces. As important, not a single Cu chisel was found on the Giza plateau. (iii) Ramps that can accommodate the range of blocks and hauling crews are projects comparable to the pyra- mids themselves; but no trace remains of the ramps. More im- portant and despite several ingenious proposals, how the ramps could have extended to the top of the pyramids has remained a vexing problem in Egyptology. 2 (2) Casing blocks, which at one time covered the pyramids, closely correspond with each other’s shape on all contact sur- faces. The currently remaining casing and backing blocks, which are just behind the former, of Khufu fit as close as 0.05 mm across their entire contiguous vertical faces in some areas and their flat outer surfaces’ angle to produce the precise slope of the rising pyramid. 3 Abd al-Latif reported that a hair would not fit between any two he was able to test. 4 Arnold 5 notes: ‘‘y the connection of the casing with the backing stones is very close and would have to be carefully prepared y. The backing stones were frequently dressed exactly to the shape of the rear face of the casing block.’’ Why such exactitude and toil would be ex- pended on areas that were to be covered for eternity is never explained. This is particularly striking considering the speed at which the Great Pyramid was built. Morris, 6 Davidovits, and Morris 7 , and Davidovits 8 provide numerous other facts that the prevailing ‘‘carve and hoist’’ model completely fails to explain but, because of lack of space, cannot be discussed herein. In the mid-1980s, Davidovits 9 proposed an alternative theory that addressed most of the aforementioned facts. He proposed the idea that the pyramid blocks were cast in situ, with a wet mix of limestone particles and a binder, tamped into molds, which in time hardened into concrete, with the macroscopic appearance and properties of native limestone. 7,8,9 According to Davidovits, the concrete is made by mixing kaolinitic limestone (like that found within the Giza plateau) with lime, plant and/or wood ash, and water. The water separates the clay from the limestone, and the basic solution, resulting from the lime/ash, dissolves the alumino-silicates. With time, the alumino-silicates react with the alkali hydroxide to form sodium and/or potassium poly-silico- oxo-aluminates, a glue he labeled a geopolymer. Egyptologists agree that while the main bulk of pyramid core blocks were made from Giza limestone, the outer and inner casings were made from a much finer-grained limestone, pre- sumed to be from the Tura formation found on the East side of the Nile. 2,10 Davidovits, 9 however, compared natural limestone samples taken from six different Tura sites with an inner casing stone from the Ascending Passageway of the Great Pyramid— the latter given to Davidovits by Egyptologist J. P. Lauer, and henceforth referred to as the Lauer sample—and showed that J ournal J. Am. Ceram. Soc., 89 [12] 3788–3796 (2006) DOI: 10.1111/j.1551-2916.2006.01308.x r 2006 The American Ceramic Society 3788 S. Weiderhorn—contributing editor ORNL is managed by UT-Battelle for the U.S. Department of Energy. This work was partially funded by the National Science Foundation (DMR 0503711). w Author to whom correspondence should be addressed. e-mail: barsoumw@drexel.edu Manuscript No. 21175. Received November 22, 2005; approved August 9, 2006.