The death of Al-Amin permitted Ali al-Ridha greater opportunity to teach.[7] In 200 AH (815–816), Ali al-Ridha was invited or forced by Al-Ma'mun to quit his home and estates in Medina and leave for the imperial capital in Khorasan. Al-Ma'mun proclaimed him as the new Imam throughout the empire upon his arrival at Merv in 201 AH (817).[2] He went further and named Ali al-Ridha as his crown prince and successor to the caliphate.[3] Following the assassination of the imperial vizier and during a relocation of the capital back to Baghdad, Ali al-Ridha died suddenly, most probably on the last day of Safar, 203 AH (September, 818).[3][lower-alpha 2] Most sources accuse Al-Ma'mun of having poisoned him.[3]