literary corpus. Although in theory Pahlavi could have been used to render any Middle Iranian language and hence may have been in use as early as 300 BC, no manuscripts that can be dated to before the 6th century AD have yet been found. Thus, when used for the name of a literary genre, i.e. Pahlavi literature, the term refers to Middle Iranian (mostly Middle Persian) texts dated near or after the fall of the Sassanid Empire and (with exceptions) extending to about AD 900, after which Iranian languages enter the "modern" stage. The oldest surviving example of the Pahlavi literature is from fragments of the so-called "Pahlavi Psalter", a 6th- or 7th-century-AD translation of a Syriac Psalter found at Bulayïq on the Silk Road, near Turpan in north-west China. It is in a more archaic script than Book Pahlavi. After the Muslim conquest of Persia, the Pahlavi script was replaced by the Arabic script, except in Zoroastrian sacred literature. The replacement of the Pahlavi script with the Arabic script in order to write the Persian language was done by the Tahirids in 9th century Khurasan. Modern times In the present day, "Pahlavi" is frequently identified with the prestige dialect of south-west Iran, formerly and properly called Pārsi, after Pars (Persia proper). This practice can be dated to the period immediately following the Islamic conquest. Script The Pahlavi script is one of the two essential characteristics of the Pahlavi system (see above). Its origin and development occurred independently of the various Middle Iranian languages for which it was used. The Pahlavi script is derived from the Aramaic script as it was used under the Sassanids, with modifications to support the phonology of the Iranian languages. It is essentially a typical abjad, where, in general, only long vowels are marked with matres lectionis (although short /i/ and /u/ are sometimes expressed so as well), and vowel-initial words are marked with an aleph. However, because of the high incidence of logograms derived from Aramaic words, the Pahlavi script is far from always phonetic; and even when it is phonetic, it may have more than one transliterational symbol per sign, because certain originally different Aramaic letters have merged into identical graphic forms – especially in the Book Pahlavi variety. (For a review of the transliteration problems of Pahlavi, see Henning.) In addition to this, during much of its later history, Pahlavi orthography was