Caliph Al Mamun, son of and successor…
676 CE to 819 CE
He invites Ali al-Ridha, known as Imam Reza, the Eighth Imam (765-816), to come from Medina to his court at Marv (Mary in present-day Turkmenistan).
While Reza is residing at Marv, Al Mamun designates him as his successor in an apparent effort to avoid conflict among Muslims.
Reza's sister, Fatima, journeys from Medina to be with her brother but takes ill and dies at Qom, in present-day Iran.
A major shrine develops around her tomb, and over the centuries Qom will become a major Shia pilgrimage site and theological center.
Al Mamun takes Reza on his military campaign to retake Baghdad from political rivals.
On this trip, Reza dies unexpectedly in Khorasan.
Reza is the only Imam to reside in, or die in, what is now Iran.
A major shrine, and eventually the city of Mashhad, grows up around his tomb, which is the major pilgrimage center in Iran.
Several theological schools are located in Mashhad, associated with the shrine of the Eighth Imam.
Reza's sudden death is a shock to his followers, many of whom believe that Al Mamun, out of jealousy for Reza's increasing popularity, had had the Imam poisoned.
Al Mamun's suspected treachery against Imam Reza and his family tend to reinforce a feeling already prevalent among his followers that Sunni rulers are untrustworthy.