No one in our day thinks of either starting or discussing such theories as these. There are, of course, several obscure points in the history of the pyramids, several details of their construction, which stimulate to fresh research and lend themselves to many different explanations; but there can be no doubt as to their general character. Their exploration and the interpretations of the Egyptian texts have confirmed the assertions of those Greek writers who were most familiar with Egypt, such as Herodotus,[177] Diodorus Siculus,[178] and Strabo.[179] The Pyramids are sepulchres. "They are massive, simply conceived, carefully sealed up tombs. All entrance is forbidden even to their most carefully built corridors. They are tombs without windows, without doors, without exterior openings of any kind. They are the gigantic and impregnable dwellings of the mummy; ... their colossal dimensions have been invoked to bear out the arguments of those who would attribute to them some other destination, but they are in fact to be found of all sizes, some being no more than twenty feet high. Besides this, it must be remembered that in all Egypt no pyramid, or rather group of pyramids, is to be found, which is not the centre of a necropolis, a fact which is enough by itself to indicate their funerary character."[180] It is proved still more definitely, if that be possible, by the sarcophagi which have been found in the internal chambers, empty in most cases, because those chambers had been entered and despoiled, either in the days of antiquity or in those of the middle ages, but sometimes intact, as in the pyramid of Mycerinus. The pyramids were hermetically sealed. Even without direct evidence we might assert that it was so, knowing as we do the precautions which the Egyptians took elsewhere to guard their tombs against intrusion; but direct proof of the fact is not wanting. When in the ninth century the Kaliph Al-Mamoun wished to penetrate into the Great Pyramid he was only enabled to do so by breaking into it violently, near the centre of its northern face, and thus stumbling accidentally upon the descending passage at some distance from its mouth. That he was reduced to employ this method at the risk of meeting with nothing but the solid masonry shows that no external indication had been left of the opening through which the mummy had been carried in. The casing seems to have been then complete and consequently the four sides of the Pyramid must have been free from _débris_ and generally uniform. That the Arabs should have chosen the right side for their attack was perhaps owing to the survival of some ancient tradition indicating the northern side to be that of the entrance, which, as a fact, it has been found to be in all the pyramids as yet explored. Perhaps too the Arabs may have been guided by the traces of previous attempts made either in the time of the Persians or in that of the Romans.[181] However this may be it is very