he sought to explain the whys and wherefores of the earliest Egyptian pyramids. Though Mendelssohn himself was not an Egyptologist, the book builds on advice from experts like Sir Robert Mond and Walter Emery, as well as his own visits to Egypt and Mexico. His principal thesis was that the pyramid at Meidum had collapsed during construction, a conclusion he arrived at using his knowledge of physics and which was sparked in 1966 by images of the Aberfan disaster, where Mendelssohn saw similarities to the rubble mound surrounding the Meidum pyramid, a primary destination for his travel to Egypt the year before. Working from that conclusion, he further elaborated a theory that pyramid construction in Egypt took on a life of its own during the Third and Fourth Dynasties, more or less independently of the reigns of pharaohs. His theory has not been taken up by the Egyptological community, but the book remains a stimulating and detailed study of the Egyptian pyramids. Mendelssohn's pyramid theory suggests explanations to a couple of mysteries in pyramid construction: Why in the time of the fourth dynasty, when all of the large Egyptian pyramids were built, there were only three Pharaohs but (with Meidum) five pyramids built. According to Mendelssohn the pyramids were constructed as cenotaphs, not as tombs and did not have to coincide with a Pharaoh's lifetime. Building of the Great Pyramids must have required a large workforce. Considering the state of perfection these pyramids show, a decisive amount of this workforce must have been highly trained professionals. Furthermore, due to the geometrical constraints, the higher a pyramid grows, the fewer people are able to work on it. If the pyramids were built independently of each other and at distinct times, it would have been necessary to assemble and train the workforce for each building and lay them off as the work continued. According to Mendelssohn, as soon as a pyramid had reached about half its final size, work started on the successor to alleviate this problem. The change of the angle seen at the Bent Pyramid can be explained as a reaction to a catastrophic collapse of the Meidum Pyramid, if these monuments were not constructed successively but with an overlap. Books by Mendelssohn The Riddle of the Pyramids. Thames & Hudson, 1974; Sphere Cardinal Edition, 1976. The Quest for Absolute Zero. McGraw-Hill, 1966. In China Now, 1969. The World of