Parts of the tribe adopted Christianity in the mid-3rd century and came under the suzerainty of the Lakhmid kings of al-Hirah, vassals of the Sasanian Empire.
[1][2] The original dwelling places of the Iyad were in the Tihama coastal area of western Arabia down to the environs of Najran.
[4] In the first half of the 3rd century CE, large groups of Iyad tribesmen migrated to Bahrayn (eastern Arabia) and formed with other Arab tribes the Tanukh confederation.
[2] From Bahrayn the tribe moved into the Sawad (fertile region of lower Mesopotamia) where they grazed their animals and utilized the Ayn Ubagh spring near Anbar as their water source.
[7] A testament to an Iyadi presence in Oriens is that the poet of the Salihid chieftain, Dawud al-Laqit, who served as the Byzantines' phylarch of the Arab tribes in its territory, was Abd al-As, a member of the Iyad.
[7] The Iyad which remained in lower Mesopotamia may have come under the suzerainty of the Lakhmid rulers of al-Hirah, vassals of the Sasanian Empire.
[2] In the early 6th century, the tribe made incursions into Sasanian territory east of the Euphrates river, prompting a punitive expedition by Khosrow I.
[8] In the Battle of Ayn al-Tamr in 633 or 634, the tribe fought under the Sasanian commander Mihran Bahram-i Chobin against the Muslim Arabs led by Khalid ibn al-Walid and again in nearby Sandawda.
[9] Caliph Umar (r. 634–644) sought their return to the Muslims' newly conquered territories and threatened to attack the Christians in his domains should Heraclius not extradite the Iyad.
[2] Members of the Iyad were also present in al-Andalus (Muslim Spain), including the well-known family of Ibn Zuhr (d.