Zoroastrianism's scriptures are the Avesta or the Zend Avesta [Pahlavi avesta = law, zend = commentary]. The Avesta consists of fragmentary and much-corrupted texts; it is written in old Iranian, a language similar to Vedic Sanskrit. The major sections of the Avesta are four—the Yasna, a liturgical work that includes the Gathas ("songs"), probably the oldest part of the Avesta and perhaps in part written by Zoroaster himself; the Vispered, a supplement to the Yasna; the Yashts, hymns of praise, including the Khurda ("little") Avesta; and the Videvdat, a detailed code of ritual purification, often erroneously called the Vendidad. Other sources of information on Zoroastrianism are Achaemenid inscriptions, the writings of Herodotus, Strabo, and Plutarch, and the commentaries on the Avesta written (6th cent. A.D.) in Pahlavi, a Persian dialect used as a priestly language, under the Sassanids.