Khilani, and the . There is no absolute dating of any Vedic text including the Atharvaveda. The dating for Atharvaveda is derived from the new metals and items mentioned therein; it, for example, mentions iron (as , literally "black metal"), and such mentions have led Michael Witzel to the estimate that the Atharvaveda hymns were compiled in the early Indian Iron Age, at, or slightly after, c. 1200/1000 BCE. corresponding to the early Kuru Kingdom. The priests who practised the Atharvaveda were considered to be the lowest tier of Brahmins, in comparison to the priests who practised the Rigveda, Samaveda, or Yajurveda. The stigma against Atharvaveda priests has continued in Odisha well into the modern day. Text The Atharvaveda is a collection of 20 books, with a total of 730 hymns of about 6,000 stanzas. The text is, state Patrick Olivelle and other scholars, a historical collection of beliefs and rituals addressing practical issues of daily life of the Vedic society, and it is not a liturgical Yajurveda-style collection. Recensions The , a later era Sanskrit text, states that the Atharvaveda had nine shakhas, or schools: , , , , , , , and . Of these, only the Shaunakiya recension, and the more recently discovered manuscripts of Paippalāda recension have survived. The Paippalāda edition is more ancient. The two recensions differ in how they are organized, as well as content. For example, the Book 10 of Paippalada recension is more detailed and observed carefully not doing a single mistake, more developed and more conspicuous in describing monism, the concept of "oneness of Brahman, all life forms and the world". Organization The Atharvaveda Samhita originally was organized into 18 books (), and the last two were added later. These books are arranged neither by subject nor by authors (as is the case with the other Vedas), but by the length of the hymns. Each book generally has hymns of about a similar number of verses, and the surviving manuscripts label the book with the shortest hymns as Book 1, and then in an increasing order (a few manuscripts do the opposite). Most of the hymns are poetic and set to different meters, but about a sixth of the book is prose. Most of the hymns of Atharvaveda are unique to it, except for the one sixth of its hymns that it borrows from the Rigveda, primarily from its 10th mandala.