The largest[2573] Pyramid is built of stone quarried in Arabia: three hundred and sixty thousand men, it is said, were employed upon it twenty years, and the three were completed in seventy-eight years and four months. They are described by the following writers: Herodotus,[2574] Euhemerus, Duris of Samos, Aristagoras, Dionysius, Artemidorus, Alexander Polyhistor, Butoridas, Antisthenes, Demetrius, Demoteles, and Apion. These authors, however, are disagreed as to the persons by whom they were constructed; accident having, with very considerable justice, consigned to oblivion the names of those who erected such stupendous memorials of their vanity. Some of these writers inform us that fifteen hundred talents were expended upon radishes, garlic, and onions[2575] alone. The largest Pyramid occupies seven[2576] jugera of ground, and the four angles are equidistant, the face of each side being eight hundred and thirty-three[2577] feet in length. The total height from the ground to the summit is seven hundred and twenty-five feet, and the platform on the summit is sixteen feet and a-half in circuit. Of the second Pyramid, the faces of the four sides are each seven hundred and fifty-seven feet and a-half in length.[2578] The third is smaller than the others, but far more prepossessing in appearance: it is built of Æthiopian stone,[2579] and the face between the four corners is three hundred and sixty-three feet in extent. In the vicinity of these erections, there are no vestiges of any buildings left. Far and wide there is nothing but sand to be seen, of a grain somewhat like a lentil in appearance, similar to that of the greater part of Africa, in fact. The most difficult problem is, to know how the materials for construction could possibly be carried to so vast a height. According to some authorities, as the building gradually advanced, they heaped up against it vast mounds of nitre[2580] and salt; which piles were melted after its completion, by introducing beneath them the waters of the river. Others, again, maintain, that bridges were constructed, of bricks of clay, and that, when the pyramid was completed, these bricks were distributed for erecting the houses of private individuals. For[2581] the level of the river, they say, being so much lower, water could never by any possibility have been brought there by the medium of canals. In the interior of the largest Pyramid there is a well, eighty-six cubits deep, which communicates with the river, it is thought. The method of ascertaining the height of the Pyramids and all similar edifices was discovered[2582] by Thales of Miletus; he measuring the shadow at the hour of the day at which it is equal in length to the body projecting it.