Khwarazmshah was an ancient title used regularly by the rulers of the Central Asian region of Khwarazm starting from the Late Antiquity until the advent of the Mongols in the early 13th-century, after which it was used infrequently. There were a total of four families who ruled as Khwarazmshahs—the Afrighids (305–995), Ma'munids (995–1017), the line of Altuntash (1017–1041), and the most prominent ones, the Anushteginids (1097–1231). Like other contemporary Central Asian titles, such as Afshin and Ikhshid, the title of Khwarazmshah is of Iranian origin. Afrighids Most of Afrighid history is recorded by the Khwarazmian scholar al-Biruni (died 1050), whose reliability has been questioned. According to the latter, the Afrighids were founded by Afrig in 305, succeeding the semi-legendary line of the Siyavushids, founded by the Iranian king Kay Khosrow. However, extensive Soviet archeological findings demonstrate that al-Biruni was in reality not well-acquainted with pre-Islamic Khwarazmian history. Coin findings show that before the advent of the Afrighids, Khwarazm was part of the Parthian Empire. The start of the Khwarazmian era seemingly took place in the early 1st-century, after they had freed themselves of Parthian rule, and established their own local dynasty of shahs. The dynastic name of "Afrighid" (Khwarazmian: ʾfryḡ) is not attested anywhere besides al-Biruni, which has led scholars to suggest that the name never existed. Likewise, many of the Khwarazmshahs recorded by al-Biruni are not supported by archeological evidence; however, this may be due to scribal errors. The Afrighids and the local population were most likely adherents of Zoroastrianism. The first Khwarazmshah to convert to Islam was Azkajwar-Abdallah, who ruled in the early 9th-century, perhaps coinciding with the reign of the Abbasid caliph al-Ma'mun (813-833). Regardless, the Islamization of the local population was much slower. In the early 10th-century, the Khwarazmshahs were made vassals of the Samanid dynasty, a Persian family which ruled mainly in Transoxania and Khurasan.