The sacred books of Persia are known by the name of "Zend-Avesta," which is an incorrect expression; we ought to say Avesta and Zend. "Avesta," like the kindred word "Veda," signifies knowledge, and the word "Zend" denotes here not the language of that name, but the "commentary" afterwards added to the original knowledge or text. The commentary is not written in the Zend language, but in Pahlavi or Persian. The Avesta, which is written in the older Zend, the sacred language of Persia, is, like other Bibles, a collection of books written in different ages, and even, it may be, in different lands. The books were brought together into one only at some period after the Christian era. The later legends as to the supernatural communication to Zoroaster of the earlier books need not detain us; we must notice, however, that the preserved books of Persian religion are held to be no more than the scanty ruins of an extensive literature. The Avesta consisted originally of 21 Nosks or books, and most of these were destroyed by Alexander when he invaded the East; only one Nosk was preserved entire. As we have it, the Avesta is a liturgical work, it contains some legends and some ancient hymns, as well as a good deal of law, but its prevailing character is that of a service-book, and it is to this that its partial preservation both at the invasion of Alexander, and at that of the Mohammedans in a later century, is probably due. It consists of three parts. The oldest is the Yasna, a collection of liturgies, which admit and indeed invite comparison with those of early Christianity: along with these are found the Gathas or hymns, the only part of the Avesta composed in verse, and written in an older dialect. The Visperad is a collection of litanies for the sacrifice; and the Vendidad is a code of early law, but contains also various religious legends. Besides these works, which constitute the Avesta proper, there is the Khorda (or small) Avesta containing devotions for various times of the day, for the days of the month, and for the religious year; these are for the use not of the priests alone but of all the faithful, and many of them are still so used.