Mamun
Abu Jaʿfar Abdullah al-Maʾmūn ibn Harun (September 13, 786 – August 9, 833) was an Abbasid caliph who reigned from 813 until his death in 833. He succeeded his brother Amin. Ma'mun conducted, in the plains of Mesopotamia, two astronomical operations intended to determine the value of a terrestrial degree. The crater Almanon on the Moon is named in recognition of his contributions to astronomy. Ma'mun's record as an administrator is also marked by his efforts toward the centralization of power and the certainty of succession. The House of Wisdom, #### was established during his reign. The scholars and the major Islamic law schools became truly defined in the period of al-Ma'mun and Sunnism, as a religion of legalism, became defined in parallel. Doctrinal differences between Sunni and Shi'a Islam began to become more pronounced. Ma'mun poisoned Imam Reza through grapes in Toos Imam Reza was buried beside the caliph's grave. Following the death of Imam Reza a great revolt took place in Khurasan, Persia. Al-Ma’mun wept and mourn for Imam Reza and tried to show himself innocent of the crime. But for all he did, he could not get himself acquitted and prove his innocence.
Sources :
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