The Avesta is the collection of the sacred texts of Zoroastrianism. Although the texts are very old, the compendium as we know it today is essentially the result of a redaction that is thought to have occurred during the reign of Shapur II (309–379 CE).
However, some portions of the collection have been lost since then, especially after the fall of the Sassanid empire in 651 CE, after which Zoroastrianism was supplanted by Islam.
The oldest existing copy of an Avestan language text dates to 1288 CE. The most ancient of the texts of the Avesta are in an old or Gathic Avestan. The majority of the texts are however from a later period: most are probably from the Achaemenid era (648–330 BCE), with a few being even younger.
All the texts are believed to have been transmitted orally for centuries before they found written form, and in existing copies, the Avestan language words are written in Din dabireh script, a Sassanid era (226–651 CE) invention. Yasna 28.1, Ahunavaita Gatha (Bodleian MS J2)The various texts of the Avesta are generally divided into topical categories, but these are by no means fixed or canonical. Some scholars prefer to place the five categories in two groups, one liturgical and the other general.
The Yasna, the primary liturgical collection. The Yasna includes the Gathas, which are thought to have been composed by Zoroaster himself.
The Visparad, a collection of supplements to the Yasna. The Yashts, hymns in honor of the divinities.
The Vendidad, describes the various forms of evil spirits and ways to confound them.
Shorter texts and prayer collections, the five nyaishes(“worship, praise”), the siroze (“thirty days”) (see Zoroastrian calendar) and the afringans (“blessings”). Some of these fragments are collected in the Khorda Avesta, the “Little Avesta”, which is the collection of texts for daily lay (as opposed to priestly) use.
Other texts of the Avesta are complemented by several secondary works of religious or semi-religious nature, which although not sacred and not used as scripture, have a significant influence on Zoroastrian doctrine. They are all of a much later date — in general from between the 9th and 12th centuries — with the youngest treatises dating to the 17th century.
Some of these works quote passages that are believed to be from lost sections of the Avesta. The most important of these secondary texts (of which there some 60 in all) are:
The D?nkard (“Acts of Religion”) in Middle Persian The Bundahishn (“Primordial Creation”) in Middle Persian The M?nog-? Khirad (“Spirit of Wisdom”) in Middle Persian The Arda Viraf N?mag (“Book of Arda Viraf”) in Middle Persian The Sad Dar (“Hundred Doors or Chapters”) in Modern Persian The Rivayats or traditional treatises in Middle and Modern Persian The use of the expression Zend-Avesta to refer to the Avesta, or the use of Zend as the name of a language or script, are relatively recent and popular mistakes.
The word Zend or Zand, meaning “commentary, translation”, refers to supplementaries in Middle Persian not intended for use as theological texts by themselves but for religious instruction of the (by then) non-Avestan-speaking public. In contrast, the texts of the Avesta proper remained sacrosanct and continued to be recited in Avestan — which was considered a sacred language. In a general sense, all the secondary texts mentioned above are also included in the Zend rubric since they too often include commentaries on the Avesta and on the religion.