The last part of the twenty year period of Imam Reza’s (A.S.) Imamah which began by his migration from Medina to Marv and lasted until his death, involves the events that are considered as the most political part of his life time. In this period, the matter of his succession to caliphate is brought up.

With regard to this fact, the political dimensions of Imam Reza’s succession to caliphate can be examined in various aspects. Here we refer to some of them: 

A) Ma’mun and the subject of succession to caliphate

There is dispute over the fact that whether Ma’mun had good will ingranting the position of succession to caliphateto Imam Reza (A.S.) or not.

Majority of the Sunni historians and researchers believe that Ma’mun had good will in granting the position of succession to caliphateto Imam Reza (A.S.). In their view, Ma’mun, who was grown up in Iran and believed in the Shia sect, sought to return the position of caliphate andWilayah to Alavid. There are some reasons for doing so in the contract which has been left from him.

In the mentioned contract, Ma’mun introduces caliphate as continuation of the Prophets’ mission and believes that the Caliph should strengthen the religion and exercise the Shariah. Then, Ma’mun regards a high stand for the position of caliphate and says the person will deserve this position who makes reconciliations between the people, unites them and prevents them from corruption. At the end of the contract, with regard to the features which he considers necessary for the successor of the caliph, Ma’mun chooses Hazrat Reza (A.S.) to be his successor and says that he is a pious, virtuous and popular person among the people.

In contrast, majority of the Shia researchers believe that the matter of Imam Reza’s succession to caliphate is due to Ma’mun’s ill intent. Ma’mun knew the spirits of the public very well and by doing so (Imam Reza’s succession to caliphate), continuation of his caliphate would be guaranteed. Concerning his behavior toward Imam Reza (A.S.), the idea of the Shia researchers is more compatible with the logic and history. 

B) Imam Reza (A.S.) and the subject of succession to caliphate

But here another question is raised that why Imam Reza (A.S.) accepted this position?

Some people believe that acceptation of this position by Imam Reza (A.S.) was out of his own free will and authority. According to these people, Imam Reza (A.S.) believed that ruling over the Islamic society is one of the rights of Iammah, so he eagerly accepted the succession to caliphate of Ma’mun.

In contrast, there is a stronger idea that not cooperating with the oppressive ruler was one of the important principles in epistemological system of Ahlul Bayt (A.S.). So Imam Reza (A.S.) never wanted to cooperate with Ma’mun but had no authority in accepting this position. Manifestation of this matter is seen in his compulsory migration to Marv at Ma’mun’s command; and Imam Reza has announced his dissatisfaction with this travel in various ways. In the contract which was concluded between the Ma’mun and Imam Reza (A.S.), Imam Reza (A.S.) repeatedly has declared his dissatisfaction with acceptance of this position by various alusions. 

C) Ma’mun’s aim of Imam Reza’s (A.S.) succession to caliphate

But the reasons of Ma’mun’s offering the Caliphate to Imam Reza (A.S.) are regarded as the important issues in the political life of Imam Reza (A.S.).

As it is inferred from studying the historical resources, Ma’mun was a very clever and cunning person who was well aware of the political situation of the Islamic towns. As a result, he had reached the conclusion that the continuation of his caliphate depended on the apparent interest and respect forKhandane -e- Esmat (pure and righteous family) (A.S.) and the Shia of this family. Thus he understood that the best possible option before him is Imam Reza (A.S.), so he invited him and forced him to come to Marv.

By doing so, Ma’mun achieved some of his political goals that include: controlling the uprise of the Shia against the ruling system, apparent removal of the Shia’s oppression (with regard to the fact that Imam Reza (A.S.) has the position of ruling and the Shia are not oppressed any more), gaining the legitimacy and acceptance for the ruling power of Abbasid, spread of the Shia’s dominance and obtaining their consent to with the Abbasidrule, destroying the spiritual personality of Imam Reza (A.S.) under the title of the caliphate successor, restraining Imam Reza’s influence among the public and sever control over him. 

D) Imam Reza (A.S.) and encountering the subject of succession to caliphate

But when Ma’mun forced the position of succession to caliphate on Imam Reza (A.S.), he didn’t take an inactive stand. Although this position was imposed on Imam Reza (A.S.), from the very beginning, he stipulated that he will accept this position provided that he would not intervene in Ma’mun’s political affairs. In addition, Imam’s speeches on his way from Medina to Marv show his dissatisfaction with accepting this position. Moreover, during his travel, Imam Reza (A.S.) repeatedly referred to the Imam’s position in the society; and in its most noticeable form, he has said that the necessary provision to be Shia is to move in the direction of Imamah; and this path was poles apart from the path of the oppressive Abbasi caliph.