If so recent a date for the construction of the American buildings be thought incompatible with this oblivion of their origin, it should be remembered how treacherous a thing is tradition, and how easily the links of the chain are severed. The builders of the pyramids had been forgotten before the time of the earliest Greek historians.[451] The antiquary still disputes whether the frightful inclination of that architectural miracle, the tower of Pisa, standing, as it does, in the heart of a populous city, was the work of accident or design. And we have seen how soon the Tezcucans, dwelling amidst the ruins of their royal palaces, built just before the Conquest, had forgotten their history, while the more inquisitive traveller refers their construction to some remote period before the Aztecs.[452] The reader has now seen the principal points of coincidence insisted on between the civilization of ancient Mexico and the Eastern hemisphere. In presenting them to him, I have endeavored to confine myself to such as rest on sure historic grounds, and not so much to offer my own opinion as to enable him to form one for himself. There are some material embarrassments in the way to this, however, which must not be passed over in silence. These consist, not in explaining the fact that, while the mythic system and the science of the Aztecs afford some striking points of analogy with the Asiatic, they should differ in so many more; for the same phenomenon is found among the nations of the Old World, who seem to have borrowed from one another those ideas, only, best suited to their peculiar genius and institutions. Nor does the difficulty lie in accounting for the great dissimilarity of the American languages to those in the other hemisphere; for the difference with these is not greater than what exists among themselves; and no one will contend for a separate origin for each of the aboriginal tribes.[453] But it is scarcely possible to reconcile the knowledge of Oriental science with the total ignorance of some of the most serviceable and familiar arts, as the use of milk and iron, for example; arts so simple, yet so important to domestic comfort, that when once acquired they could hardly be lost.