Abū al-ʿAbbās Abd Allāh ibn Hārūn al-Maʾmūn (Arabic: أبو العباس عبد الله بن هارون الرشيد, romanized: Abū al-ʿAbbās ʿAbd Allāh ibn Hārūn ar-Rashīd; 14 September 786 – 9 August 833), better known by his regnal name al-Ma'mun (Arabic: المأمون, romanized: al-Ma'mūn), was the seventh Abbasid caliph, who reigned from 813 until his death in 833.

He succeeded his half-brother al-Amin after a civil war, during which the cohesion of the Abbasid Caliphate was weakened by rebellions and the rise of local strongmen; much of his domestic reign was consumed in pacification campaigns.

Well educated and with a considerable interest in scholarship, al-Ma'mun promoted the Translation Movement, the flowering of learning and the sciences in Baghdad, and the publishing of al-Khwarizmi's book now known as "Algebra".

He is also known for supporting the doctrine of Mu'tazilism and for imprisoning Imam Ahmad ibn Hanbal, the rise of religious persecution (mihna), and for the resumption of large-scale warfare with the Byzantine Empire.

[1] Marajil died soon after his birth, and Abdallah was raised by Harun al-Rashid's wife, Zubayda, herself of high Abbasid lineage as the granddaughter of Caliph al-Mansur (r. 754–775).

Muhammad received the oath of allegiance (bay'ah) with the name of al-Amin ("The Trustworthy"), first in Khurasan by his guardian, the Barmakid al-Fadl ibn Yahya, and then in Baghdad.

[2][7] Very quickly, the latent rivalry between the two brothers had important repercussions: almost immediately after the court returned to Baghdad in January 803, the Abbasid elites were shaken by the abrupt fall of the Barmakid family from power.

[2] The years after the fall of the Barmakids saw an increasing centralization of the administration and the concomitant rise of the influence of the abnāʾ, many of whom were now dispatched to take up positions as provincial governors and bring these provinces under closer control from Baghdad.

Lawlessness in Baghdad led to the formation of neighborhood watches with religious inspiration, with two notable leaders being Khalid al-Daryush and Sahl ibn Salama al-Ansari.

"Most" of the leadership of this vigilante movement came from the sulaahd ("men of good will of the neighborhoods and blocks") and from "popular preachers" (as both Khalid al-Daryush and Sahl ibn Salama al-Ansari were); its followers were called the 'amma, (the common people).

[15] According to Shia sources, the deposing of al-Ma'um in Baghdad was not out of opposition to the wise and pious Imam Reza, but because of rumors spread by Fazl ibn Sahl.

Al-Ma'mūn ordered that the Imam be buried next to the tomb of his own father, Harun al-Rashid, and showed extreme sorrow in the funeral ritual and stayed for three days at the place.

In AH 210 (825–826 CE) Abdullah ibn Tahir al-Khurasani secured Egypt for al-Ma'mun, freeing Alexandria from Andalusians and quelling unrest.

Forced to deal with the rebel Thomas the Slav, Michael had few troops to spare against a small Andalusian invasion of 40 ships and 10,000 men against Crete, which fell in 824 AD.

The Caliph replied that he carefully considered the Byzantine ruler's letter, noticed it blended suggestions of peace and trade with threats of war and offered Theophilos the options of accepting the shahada, paying tax or fighting.

[21] As part of his peace treaty with the Byzantine Emperor, al-Ma'mun was to receive a number of Greek manuscripts annually, one of these being Ptolemy's astronomical work, the Almagest.

al-Ma'mun once defeated a Byzantine Emperor in a battle and as a tribute, he asked for a copy of Almagest, Ptolemy's Hellenistic compendium of thoughts on astronomy written around AD 150.

Mu'tazili theology was deeply influenced by Aristotelian thought and Greek rationalism, and stated that matters of belief and practice should be decided by reasoning.

This opposed the traditionalist and literalist position of Ahmad ibn Hanbal and others, according to which everything a believer needed to know about faith and practice was spelled out literally in the Qur'an and the Hadith.

[27] Al-Tabari (v. 32, p. 231) describes al-Ma'mun as of average height, light complexion, handsome and having a long beard that lost its dark colour as he aged.

He relates anecdotes concerning the caliph's ability to speak concisely and eloquently without preparation, his generosity, his respect for Muhammad and religion, his sense of moderation, justice, his love of poetry and his insatiable passion for physical intimacy.

Ibn Abd Rabbih in his Unique Necklace (al-'iqd al-Farid), probably drawing on earlier sources, makes a similar description of al-Ma'mun, whom he described as of light complexion and having slightly blond hair, a long thin beard, and a narrow forehead.

Described as charming with fair skin, she was praised for her musical talent, particularly her skill in playing instruments, and was known for her exceptional ability as a songwriter and singer.

[44] According to the account of al-Tabari, on his deathbed al-Ma'mun dictated a letter nominating his brother, rather than al-Abbas, as his successor,[45] and Abu Ishaq was acclaimed as caliph on 9 August, with the Laqab of al-Mu'tasim (in full al-Muʿtaṣim bi’llāh, "he who seeks refuge in God").

[46] It is impossible to know whether this reflects actual events, or whether the letter was an invention and Abu Ishaq merely took advantage of his proximity to his dying brother, and al-Abbas's absence, to propel himself to the throne.

Only when al-Abbas refused them, whether out of weakness or out of a desire to avoid a civil war, and himself took the oath of allegiance to his uncle, did the soldiers acquiesce in al-Mu'tasim's succession.

[53] Other arguments were that: the Caliphate's official black colour was changed to the Prophetic green; in 210 AH/825 CE, he wrote to Qutham b. Ja'far, the ruler of Medina, to return Fadak to the descendants of Muhammad through his daughter, Fatima; he restored nikah mut'ah, previously banned by Umar ibn al-Khattab, but practiced under Muhammad and Abu Bakr; in 211 AH/826 CE, al-Ma'mun reportedly expressed his antipathy to those who praised Mu'awiya I, the founder and first caliph of the Umayyad Caliphate, and reportedly punished such people;[54] this later view of al-Suyuti however is questionable since it contradicts the fact that al-Ma’mun promoted scholars who openly defended Muawiyah, such as the Mu’tazilite scholar Hisham bin Amr al-Fuwati, who was a well-respected judge in the court of al-Ma’mun in Baghdad;[55] in 212 AH/827 CE, al-Ma'mun announced the superiority of Ali ibn Abu Talib over Abu Bakr and Umar b. al-Khattab;[54] in 833 CE, under the influence of Muʿtazila rationalist thought, he initiated the mihna ordeal, where he accepted the argument that the Quran was created at some point over the orthodox Sunni belief that the Book is the uncreated word of God.

[57] Al-Ma'mūn ordered that al-Ridha be buried next to the tomb of his own father, Harun al-Rashid, and showed extreme sorrow in the funeral ritual and stayed for three days at the place.

Muhammad al-Jawad, Ali al-Ridha's son and successor, lived unopposed and free during the rest of al-Ma'mūn’s reign (till 833 CE).

According to Ya'qubi, al-Ma'mun gave al-Jawad one hundred thousand dirham and said, "Surely I would like to be a grandfather in the line of the Apostle of God and of Ali ibn Abu Talib.