Imam Reza (A.S), the Eighth Imam of the Shiite Muslims, was born there in Medina historians are not sure about. His birth day, month and year or they may know it completely but they don’t acknowledge-History has never been a good trustee-and His birth was declared in the years 148,151,153 and the days; on Friday in Ramadan 19th (the ninth month of Arabic lunar year), in the half of Ramadan month, on Friday in Rajab 10 th (the seventh month of Arabic lunar year) and Zilgha’deh 11th (twelfth month of Arabic lunar year).But the very year 148 namely Imam Ja’far-e- Sadegh’s (AS) Martyrdom year is more certain than the above-mentioned years. This is certainly the year that the distinguished scholars such as Mofid, Kalimi, Kafa’mi, Shahid Sani-e-Tabarsi, Sadough, Ebn-e-Zohreh, Mas’oudi, Abo’l-Fada, Ebn-e-Athir, Ebn-e-Hojar, Ebn-e-Jouzi and the other scholars have approved as the Imam Reza’s (AS) birth year. But His Holy titles and nicknames have been remained in history’s mind-maze such shining words. His nickname is Abo’l-Hasan and His titles are Saber, Zakki, Vali, Fazel, Vafi, Seddigh, Razi, Serajo’llah, Nouro’l-Hoda, Ghorrato’l-Eino’l-Mo’menin, Kelidato’l-Mohedin, Kafo’l-Malek, Kafia’l-Khalgh, Rabbo’ssarir, and Ra’abo’l-Tadbir.
And Reza (AS) is the most well-known title that we have known Imam by this during the history. Perhaps you want to know the reason of this title:
“He was called ‘Reza’ because He was pleasant in the heavens and prophets and God and the Imams after Him were pleased with Him, upon the Earth. Also, it is said that: because all persons who agreed or disagreed with Him, both groups were pleased with Him and finally they have called Him “Reza” because Ma’moun became pleased with Him, too.”
When you read His mother’s names, titles and sobriquets, you feel something inside them just like whatever is in Imam Reza’s (AS) titles: Ommo’l-Banin, Najmeh, Sakan, Toktam, Kheizaran, Tahereh, Shaghra’.
Although according to a narration, 5 boys and one girl has been mentioned for Imam Reza (AS), but as Allameh Majlesi has told: Javad was regarded as the only Imam Reza’s child- a familiar name for us-…the only subject that has remained is Imam Reza’s martyrdom year that again history can’t help us about it properly and the possibilities are the years 202, 203 and 206 Anno Hejira. But most of scholars have considered the year 203 as His martyrdom year. Hence the age of Imam Reza (AS) was 55 years old at the time of martyrdom. He has spent 25 years of His lifetime with His father and He undertook the Shiite’s leadership for 20 years.
The beginning of Imam Reza’s (AS) leadership is coincided with the final period of Harouno-e-Abbassi’s caliphate for 10 years.
Five years later, His leadership is also coincided with Amin’s caliphate and finally a period of Ma’moun’s caliphate for 5 years as well as his dominance on Islamic territory of that period.
…Ma’moun the very person, who martyred Imam with poison conspiratorially and Imam’s followers, buried His holy body in Tous (in Harouni’s Gheble-ye-Ghobbeh); the dome of Hamid-ebne-Ghahtabe-ye-Taei and today His sepulcher's dust is the vitriol of the enamored people’s eyes.

In Medina;
The periods of Imam Reza’s (AS) leadership in Medina had started by the year 183 Anno Hejira .Those days Harouno’Rashid had control over the political government that have been administered in Baqdad. Haroun’s dissertation was torture, prison and killing as like as all history’s oppressive. His soldiers persecuted Muslims to pay exorbitant taxes.
As he incarcerated Imam Mousa’bne Ja’far (AS); Imam Reza’s father, in the prisons of Baqdad and Basra and finally brutally martyred Him with poison. That is to say the periods that the tragedy of His father’s martyrdom was happened as well as lamentable tragedies for Alavian.
In the period of Imam Reza(AS) Harouno’Rashid was so anxious of Ahle-Beit’s influence on people, besides these, he tried to dictate deviated reflections and thoughts into Muslims’ science in order to draw their attention to a distorted Islamic school, leaving the household of the holy prophet (S.A.W.A) in a theoretical seclusion.
Aboubakr-e-Kharazmi (in 383 Anno Hejira) in a letter to Neishabour’s people describes how harshly the Abbasids' ruler-Haroon-, in particular, behaved. He writes: Haroon, undermining the prophetic mission and ignoring Imam at (Divine Leadership), died. when one of the Imams of the house hold of the Holy prophet (S.A.W.A) passed away, no one participated in his/her funeral procession, and plastered his/her burial chamber, but when a zany or a juggler or a minstrel or a killer of them died, officials and judges used to attend upon his corpse and leaders and governors used to mourn for the dead. Secularist and sophist were safe in their country and they didn’t oppose against those who taught the philosophical books, but they ruthlessly killed the Shiite Muslims, and also those Muslims who chose "Ali" for their son's name, were brutally killed and beheaded by the rulers, agents."
Considering these cases and dominant atmosphere, Imam Reza (AS) preferred not to declare and publicize His Imamate and He communicated only with a few of His followers. But in the course of years, when Haroun’o-Rashid’s government grew weak because of different rebellions, Imam Reza (AS) announced His divine leadership (Imamate) openly and proceeded to solve people’s problems in the social and religious fields. His Holiness says: “I was attending in mourning ceremony of my ancestor; the Holy Prophet (S.A.W.A) while there were so many of erudite and scholars Medina. When one of them could not find a solution for a question, they all addressed me those questions and I was answering their questions.” Haroon-ar-Rashid died in 193 Anno Hejira 809 (A.D), on his way to khorasan intending to suppress the rebellions of the region. He was buried in Sanabad-e-Tous within an inferior room in Tous’ governor palace “Hamid-ebne- Ghahtabeye Taei”. Haroun’s sons “Amin and Ma’moun” quarreled with one another to grab power. Amin was dominant in Baqdad and Ma’moun ascended the throne in Marv. Hatred and discrepancy flamed up within the two brothers for five years and finally Ma’moun’s corps attacked Baqdad; and killed Amin in the year 198 Anno Hejira and Ma’moun kept control over the government completely. Since the Alawids and the Sadat, descendants of the Holy prophet (S.A.W.A) were driven to extremities of Haroon's and his sons' cruelties, they revolted.
As a result of this, people started to rebel in the regions of Iraq, Hejaz and Yemen. They wanted only one thing: the government should be controlled by Mohammad’s (AS) dynasty. In order to quell the rebellions and keep his position as the ruler of the country, Mamoon decided to invite the socio-religious leader of the Shiite Muslims - Imam Reza (A.S) - , to Khorasan.
The first question when reviewing this historical event is always this: WHY? What was the plot of Ma’moun?
That is why to ratify his activities and policies beside Imam. Imam Reza (AS) did not accept his so-called sincere invitations until Ma’moun started to threat seriously. The Historical documents would not testify the first fields of Imam’s journey and many details of preliminaries Razavi’s Hijrat has remained unsaid and put under the veil of ambiguity. But by studying the given documents the truth will be revealed that there are some previous correspondences between Marv and Medina, and the emphasis was on the Imam’s journey to Marv. Ma’moun in addition to the invitations, sent two persons of his officials by names “Reja-ebne-Abi Zahhak and Yaser Khadem” to Medina. After entering Medina, they introduced their mission as follows: “Ma’moun has commanded and appointed us to carry you to Khorasan.” Imam Reza (AS) was a person who was aware of Ma’moun’s deceits and also knew his conspiracies and manners. Imam Reza (AS) could remember his Father, who was in prisons for a long time, with all their bitterness and pain and he knew that Ma’moun is a person that kills his brother and currently he couldn’t calm down because of
Imam’s presence among people. So Imam Reza (AS) started his journey. An unwilling journey and He should bid farewell to Medina unhappily, a farewell to the holy mausoleum of the Holy Prophet (S.A.W.A), a farewell to people who loved Him. He was a kind father for Medina’ inhabitants. He didn’t need a geographical journey. He had gone on a journey to the hearts’ geography. Anyway, Imam started the journey though he disliked it and when he went, he knew well what Ma’moun would do towards Him, and was completely aware that He will be eternal in people’s heart.

From Medina to Marv
It was too hard for Imam (AS) to leave Medina. Even if once in your lifetime you were a passenger of a strange land, you should understand this feeling; like Yusuf who was a stranger from Medina to Marv and Egypt and in view of the fact that He was wealthy and rich gloriously, but He liked to come back to Kan’an. Imam Reza (AS) bade farewell to the Prophet’s Mosque while He knew that He never come back. Sheikh Saddough has quoted in Oyoon Akhbar'al Reza from Mohaval-e-Bajestani, under his own documentary: “Imam Reza (AS) bade farewell to the Holy Prophet (PBUH), but every time He looked towards the tomb, He cried tearfully.” I approached Imam (A.S) and offered Him my congratulations. Imam said: “set me free! I will leave my ancestor’s vicinity ((Mohammad PBUH)) and I will die in a strange land”. Whatever is clear to all of us is the beginning and the termination of Imam Reza’s (AS) journey, but the fact that what courses exactly He passed through in the space of the two points is not clear and there is some diversity of opinions about that. It is hard to distinguish the exact course of Imam Reza’s (AS) journey because there are so many different reports or sometimes we see contradictory source about His journey.

Source: aqr