Battle of Ray (811)

Ultimately al-Amin declared that his sons would reign as Caliphs after he had died, even going as far as to seize the documents binding the brothers to the agreement from the sacred city of Mecca.

Al-Ma'mun was much angered by this and prepared for war, his vizier sending a force to defend the key frontier stronghold of Rayy, between the Zagros and Elburz mountain ranges.

Al-Ma'mun's army was led by Tahir ibn Husayn, a Persian noble with some claim to one of the many mountain principalities which were nominally vassals to the caliphate.

Fearing what the citizens would do to rid themselves of his force if he chose to remain within Rayy's walls and defend against a siege, Tahir led his army along the road towards Baghdad until the intruders were in sight.

Then the main battle began, with a lightning attack force of 700 Khwarazmians, backed by archers, sent to smash the centre of Ali's army, and if possible destroy its command structure.