It was in these characters that some time during the Sassanian dynasty the Zend-Avesta, or sacred books of the Persians, were transcribed in the ancient speech of their origin, which have thus been preserved to the present day by the surviving representatives of this ancient faith. The language expressed in the Gathas, or hymns, the most archaic portions of the Avesta, is in the ancient vernacular of eastern Persia; sometimes called “Old Bactrian,” and is the most archaic of Iranian dialects. This was apparent when Sanskrit became known to European scholars. The striking resemblance of the Gathas to the older Sanskrit of the “Vedic Hymns,” indicated a close relationship. They seemed, indeed, like two dialects of the same speech. In fact, the readiness with which this old Persian was converted into pure Sanskrit by a few slight phonetic changes, verified these indications. In the further comparative study of the older Sanskrit with this older Persian, it was found that while the Sanskrit may be regarded as the older brother of the Aryan group, this ancient Persian is in some respects more archaic. It nevertheless remains that the Sanskrit is in the main the elder representative of this family of languages, retaining the characteristic forms of phonetic structure once common to the whole family, with their meanings less changed, than any other branch of the Aryan group. It is this fact which enabled philologists to base a science of Aryan philology upon the Sanskrit. And not only this, but from which has arisen the science of comparative philology for all families of languages. Whatever may be said of the ethnic affinities of the Aryans, or their primitive home, this much has been made evident in the comparative study of the Vedas and the Avesta; that there is close kinship here. They tell of a time not so remote in history as that of older Chaldea or Egypt, when these Indo-Iranians were one people, with a common ancestry, inhabiting the same country, speaking the same language, with the same social institutions and the same beliefs. They indicate that the home of these Indo-Iranians, before their separation, was somewhere near the head waters of the Oxus, to the north-west of the Hindu-Kush. That finally there was a separation of these families, those afterwards known as the Hindus penetrating these great mountain passes into the Punjaub, “The land of the Five Rivers,” in the northwestern part of India, from whence they spread southward over this great peninsula. The other branch, the Iranians, remained for a time north of the Hindu-Kush in Bactria, which formed later on a part of the ancient empire of Iran, or Persia, on the northeast.