A Brief Introduction in to the Life of Imam Sajjad (ʹa)
Imam Sajjad (ʹa) was the son of Imam Husayn ibn ‘Ali (ʹa), the third Imam of the Shia world, and his mother was Shahr Bānūwīyah. He is most famously known by his agnomens Zayn al-Abidin and Sajjad.
Imam Sajjad (ʹa) was born in the year 28 Hijrī and he spent the period of his youth in the city of Medina. He was alive for 2 years during the rule of his grandfather, Amīr al-Muʹminīn (ʹa), and after that, he witnessed 10 years of the Imamate of his uncle, Imam Hasan (ʹa); during this time, Imam Hasan (ʹa) was the caliph of the Muslims for a period of 6 months. After the martyrdom of Imam Hasan (ʹa) in the year 50 Hijrī, he witnessed 10 years of the Imamate of his father, Imam Husayn (ʹa). The last years in the Imamate of Imam Husayn (ʹa) coincided with the peak of Mūʹāwīya’s political power and were filled with constant altercations; Imam Zayn al-Abidin (ʹa) was witness to all of these events.
In the month of Muḥarram, in the year 61 Hijrī, Imam Zayn al-Abidin (ʹa) was present at the revolt of Karbala and the martyrdom of Imam Husayn (ʹa) and his companions which followed. After the tragedy of Karbala, in which the Imamate was transferred to him, the Imam (ʹa) and the rest of the captives were first taken to Kūfah and then to Syria. During this journey, he was the guardian and support of the rest of the group during the hard times and difficulties which they constantly encountered. During this journey, Imam Zayn al-Abidin (ʹa) disgraced the government of Yazīd through his fiery and emotion-evoking sermons. After leaving Syria, he took up Medina as his place of residence. This continued until he was martyred in the year 94 or 95 Hijrī. He was buried in the graveyard of Baqīʹ, next to the grave of his uncle Imam Hasan (ʹa).
Caliphs Who Lived Contemporaneously With the 4th Imam (ʹa)
Imam ‘Ali ibn al-Husayn (ʹa) lived contemporaneously with the following caliphs:
1- Yazīd ibn Mūʹāwīya (61-64 Hijrī)
2- ʹAbdullah ibn Zubayr (61-73 Hijrī)
3- Mūʹāwīya ibn Yazīd (A few months in the year 64 Hijrī)
4- Marwān ibn Ḥakam (9 months in the year 65 Hijrī)
5-ʹAbd al-Malik ibn Marwān (65-86 Hijrī)
6- Walīd ibn ʹAbd al-Malik (86-96 Hijrī) 
 Muḥammad ibn Yaʹqūb Kulaynī, Ūṣūl al-Kāfī, Researched and edited by: ‘Ali Akbar al-Ghaffārī, Tehran, Maktabah al-Ṣādiq, 1381 Hijrī Qamarī, vol. 1, p. 467; Shaykh Mufīd, al-ʹIrshād, Qum, Maktabah Baṣīratī, p. 253; Faḍl ibn Hasan Ṭabarsī, ʹIʹlām al-warā bi ʹiʹlām al-hudā, Ṭabʹat al-Thālitha, Tehran, Dār al-Kutub al-Islāmīyah, p. 256; Hasan ibn Muḥammad ibn Hasan Qummī, The History of Qum, translated by Hasan ibn ‘Ali ibn Hasan Qummī, edited by: Sayyid Jalāl al-Dīn Tehrānī, Tehran, Tūs Publications, 1361 Hijrī Qamarī, p. 196; ‘Ali ibn ʹĪsā ʹIrbilī, Kashf al-ghammah fī marifat al-ʹaʹimmah, Tabriz, Maktabah Banī Hāshimī, 1381 Hijrī Qamarī, vol. 2, p. 286. In the books of history and the books regarding the lives of the Imams (‘a), the name of the mother of the 4th Imam (‘a) is one of which there are varying accounts. In addition to Shahr Bānūwīyah, there are an additional 12 names, which she has been called as well. These are namely: Shahi Zanān, Jahān Shah, Shahr Nāz, Jahān Bānūwīyah, Khawlah, Salāfah, and so on… For further information on this matter, refer to: Doctor Shahīdī, Sayyid Jaʹfar, The Life of ‘Ali ibn al-Husayn (‘a), First Print, Tehran, The Office for the Propagation of Islamic Culture, 1365 Hijrī Qamarī, p. 27-29; Doctor Karīmān, Husayn, Ray Bāstān, Second Print, Tehran, The Publications Office of the National University of Iran, vol. 1, p. 403-416.  Shaykh Mufīd, al-ʹIrshād, Qum, Maktabah Baṣīratī, p. 253; ʹAllāmah Ṭabarsī, Tāj al-mawālīd (part of a collection called Majmūʹah Nafsīyah), Maktabah Baṣīratī, p. 112; Shaykh Mufīd, Masārr al-Shīʹah (part of the same collection), p. 67; Muḥammad ibn Jarīr ibn Rustam Ṭabarī, Dalāʹīl al-imāmah, al-ṭabʹat al-thālithah, Qum, Rāḍī Publications, 1363 Hijrī Qamarī, p. 80; Muḥammad ibn Yaʹqūb Kulaynī, Ūṣūl al-kāfī, Researched and edited by: ‘Ali Akbar al-Ghaffārī, Tehran, Maktabah al-Ṣādiq, 1381 Hijrī Qamarī, vol. 1, p. 466; Sibṭ ibn Jawzī, Tadhkirah al-khawāṣ, Najaf, Manshūrāt al-Maṭbaʹah al-Ḥaydarīa, 1383 Hijrī Qamarī, p. 324; Masʹūdī, Ithbāt al-waṣīyah, al-ṭabʹat al-rābiah, Najaf, al-Maṭba’at al-Ḥaydarīa, 1373 Hijrī Qamarī, p. 167; Fattāl Nayshābūrī, Rawḍat al-wāʹīẓīn, Researched and Compiled by: al-Shaykh Husayn al-ʹAlamī, al-ṭabʹat al-ʹūlā, Beirut, Muʹasasat al-ʹAlamī Lil Maṭbūʹāt, 1406 Hijrī Qamarī, p. 222; Faḍl ibn Hasan Ṭabarsī, ʹIʹlām al-warā bi ʹiʹlām al-hudā, Ṭabʹat al-Thālitha, Tehran, Dār al-Kutub al-Islāmīyah, p. 256; Ibn Abī al-Thalaj al-Baghdādī, Tārīkh al-ʹaʹimmah (part of the Nafsīyah Collection), Qum, Maktabah Baṣīratī, p. 9. Some historians believe that Imam ‘Ali ibn al-Husayn’s (‘a) birthday was in the year 36 or 37 Hijrī.
 The time period mentioned, signifies the time that they ruled during the Imamate of Imam Sajjad (‘a). They are not inclusive of their entire period of rule.  ʹAbdullah ibn Zubayr was of the small number of individuals who had not given the oath of allegiance to Yazīd. After the death of Mūʹāwīya, and a little time before the departure of Imam Husayn (‘a) to Mecca, he entered the city and became engrossed in political activities. After the martyrdom of Imam Husayn (‘a), since he had no other rivals in the lands of the Ḥijāz, he gathered some supporters and announced himself as the caliph. Yazīd, up to the very end of his life, was unable to defeat him, and he ruled in Mecca until 73 Hijrī. ʹAbdullah conquered the Ḥijāz, Iraq, Egypt, and part of the eastern Muslim lands, and the successor of Yazīd was only able to rule Syria and some other limited areas. Therefore, from the year 61 until 73 Hijrī, the Muslim lands were ruled by 2 separate rulers, who each had their own spheres of power. Later on, ʹAbdullah ibn Zubayr was defeated and killed by the forces of ʹAbd al-Malik (in the year 73 Hijrī). After this, all of the Muslim lands were ruled under the government of the Marwanids, and Syria was once again considered as the center of rule.  Taken from the text: Sīrah Pīshvāyān, Mahdī Pīshvāī, Muʹasasah Imam Sadiq (ʹa), Qum, 1390 Hijrī Shamsī, 23rd Edition, p. 233.