How all this was done is one of the enigmas of modern science. It has been generally believed that inclined planes of earth were used to enable the workmen to raise the huge stones to their places, the earth being cleared away afterward. But it is possible that the ancients had a more extended knowledge of mechanical powers than we usually give them credit for, and that they made use of machinery very like that employed by moderns for lifting great weights. Large cavities are found in some of the stones in the pyramids, which may have been worn by the foot of a derrick turning in them. That there were enormous numbers of men employed in the building of these ancient structures is well known; these results of their great aggregated strength we see, but they left no record of the means by which this strength was focused and brought most effectually to bear on their mighty tasks.