Year 821 (DCCCXXI) was a common year starting on Tuesday of the Julian calendar.
The 800s decade ran from January 1, 800, to December 31, 809.
The 810s decade ran from January 1, 810, to December 31, 819.
The 820s decade ran from January 1, 820, to December 31, 829.
The 830s decade ran from January 1, 830, to December 31, 839.
The 780s decade ran from January 1, 780, to December 31, 789.
The 760s decade ran from January 1, 760, to December 31, 769.
Year 802 (DCCCII) was a common year starting on Saturday of the Julian calendar.
Year 758 (DCCLVIII) was a common year starting on Sunday of the Julian calendar. The denomination 758 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
Year 785 (DCCLXXXV) was a common year starting on Saturday of the Julian calendar. The article denomination 785 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years. It is still used today in this manner.
Year 836 (DCCCXXXVI) was a leap year starting on Saturday of the Julian calendar.
Abu al-Abbas Abdallah ibn Harun al-Rashid, better known by his regnal name al-Ma'mun, 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.
Abū Muḥammad Mūsā ibn al-Mahdī al-Hādī better known by his laqab al-Hādī (الهادي) was the fourth Arab Abbasid caliph who succeeded his father al-Mahdi and ruled from 169 AH until his death in 170 AH. His short reign ended with internal chaos and power struggles with his mother.
The Fourth Fitna or Great Abbasid Civil War resulted from the conflict between the brothers al-Amin and al-Ma'mun over the succession to the throne of the Abbasid Caliphate. Their father, Caliph Harun al-Rashid, had named al-Amin as the first successor, but had also named al-Ma'mun as the second, with Khurasan granted to him as an appanage. Later a third son, al-Qasim, had been designated as third successor. After Harun died in 809, al-Amin succeeded him in Baghdad. Encouraged by the Baghdad court, al-Amin began trying to subvert the autonomous status of Khurasan, and al-Qasim was quickly sidelined. In response, al-Ma'mun sought the support of the provincial élites of Khurasan and made moves to assert his own autonomy. As the rift between the two brothers and their respective camps widened, al-Amin declared his own son Musa as his heir and assembled a large army. In 811, al-Amin's troops marched against Khurasan, but al-Ma'mun's general Tahir ibn Husayn defeated them in the Battle of Ray, and then invaded Iraq and besieged Baghdad itself. The city fell after a year, al-Amin was executed, and al-Ma'mun became Caliph.
Harthama ibn A'yan was a Khurasan-born general and governor of the early Abbasid Caliphate, serving under the caliphs al-Hadi, Harun al-Rashid and al-Ma'mun. He played an important role in the victory of al-Ma'mun in the Abbasid civil war, but was executed at his orders when he protested against the power of the Sahlid family that dominated his court.
Ali ibn Isa ibn Mahan was a prominent Iranian military leader of the Abbasid Caliphate in the late 8th and early 9th centuries.
The Battle of Fakhkh was fought on 11 June 786 between the forces of the Abbasid Caliphate and the supporters of a pro-Alid rebellion in Mecca under al-Husayn ibn Ali, a descendant of Hasan ibn Ali.
Muḥammad ibn Sulaymān ibn ʿAlī ibn ʿAbd Allāh ibn ʿAbbās was a member of the Abbasid dynasty who served as provincial governor of Kufa and Basra and its dependencies in the Persian Gulf for most of his life. He also played a leading role in the suppression of the pro-Alid uprisings of 762–763 and 786, and helped ensure the peaceful accession of Caliph al-Mahdi in 775. His enormous fortune was confiscated after his death by Caliph Harun al-Rashid.
Al-Ḥusayn ibn ʿAlī al-ʿĀbid was an Alid who rebelled at Medina against the Abbasid caliph al-Hadi. He was killed with many of his followers at the Battle of Fakhkh outside Mecca on 11 June 786, whence he is known to history as the Man of Fakhkh.
