A more curious but equally deliberate effect could be observed on the equinoxes, 20 March and 22 September. Then the passage of the sun’s rays from south to north resulted at noon in the progressive obliteration of a perfectly straight shadow that ran along one of the lower stages of the western façade. The whole process, from complete shadow to complete illumination, took exactly 66.6 seconds. It had done so without fail, year-in year-out, ever since the pyramid had been built and would continue to do so until the giant edifice crumbled into dust.7
