Avesta word for "praise-song" (Bartholomae: "Lobgesang"); that word is not actually attested in any text. The surviving texts of the Avesta, as they exist today, derive from a single master copy produced by Sasanian Empire-era (224–651 CE) collation and recension. That master copy, now lost, is known as the 'Sassanian archetype'. The oldest surviving manuscript ("K1") of an Avestan language text is dated 1323 CE. Summaries of the various Avesta texts found in the 9th/10th century texts of Zoroastrian tradition suggest that a significant portion of the literature in the Avestan language has been lost. Only about one-quarter of the Avestan
Avesta collection now lies in the Royal Library, Denmark ('K'-series). Other large Avestan language manuscript collections are those of the British Museum ('L'-series), the K. R. Cama Oriental Library in Mumbai, the Meherji Rana library in Navsari, and at various university and national libraries in Europe. In its present form, the Avesta is a compilation from various sources, and its different parts date from different periods and vary widely in character. Only texts in the Avestan language are considered part of the Avesta. According to the "Denkard", the 21 "nask"s (books) mirror the structure of the 21-word-long "Ahuna Vairya" prayer: each