This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
The Fourth Fitna was a civil war between the sons of the Abbasid caliph Harun al-Rashid over succession to the caliphate following his own death in 809. Harun had divided the empire's administration between his two sons during his own lifetime, naming al-Amin caliph in Baghdad while granting al-Ma'mun a wide autonomous governorship over Khurasan in the east, an arrangement that collapsed into open war once al-Amin attempted to name his own son heir instead of honoring al-Ma'mun's own already established succession rights.
Al-Ma'mun's general Tahir ibn Husayn led a prolonged campaign westward from Khurasan, culminating in a year long siege of Baghdad itself. The city fell to Tahir's forces in September 813 after a devastating siege that badly damaged much of Baghdad, and al-Amin himself was captured and executed, leaving al-Ma'mun as sole caliph over an empire his own family's war had left visibly weakened and materially damaged. Baghdad itself, built only a few decades earlier as the Abbasid dynasty's own showcase capital, bore the physical cost of the siege directly, and observers at the time described a city whose grandest quarters had been reduced to ruin by the very civil war fought to decide who would rule it.