Another instance of a deity who is scarcely changed in any way is Mithra, the Sanskṛit form of which is Mitra. In the Ṛig-veda “Mitra calls men to their work; Mitra is preserving earth and heaven; Mitra looks upon the nations always without shutting his eyes.” In the Avesta he is also the lord of the morning, the god of day, and the object of profound adoration. These are but a few out of many similarities, and the careful student of the Veda and the Avesta will also notice the identity of many terms referring to priestly functions. The very name of “priest” in the Zend- Avesta is _atharva_, and it is merely another form of _atharvan_, which is the term applied to the priest of fire and Soma, in the Vedas.[290] These and many other similarities do not necessarily prove that the Zend-Avesta was partially copied from the Veda, but they do prove that “the Veda and the Zend-Avesta are two rivers flowing from one fountain head; the stream of the Veda is the fuller and purer, and has remained truer to its original character; that of the Zend-Avesta has been in various ways polluted, has altered its course, and cannot, with certainty, be traced back to its source.”[291] Nevertheless, their common origin must be assigned to the early Indo-Īraniān traditions. Besides the official copy of the sacred books, which was burned by Alexander with the palace of the Persian king at Persepolis, there were other copies, or at least portions of them, and these the first Sassanian kings collected, and compiled from them, as far as possible, their sacred literature. For more than five centuries after Alexander, the empire of Persia suffered from foreign despotism and internal dissensions, but during this long period of political unrest, the Sassanian kings were able to collect a large proportion of the old writings, even though the literature which was thus restored consisted chiefly of fragments; it appears, however, that some portion of nearly every book was recovered by the zeal of these monarchs, and therefore the total disappearance of some of them must be assigned to more recent times.