The Iyad (Arabic: إياد, romanized: Iyād) were an Arab tribe which dwelt in western lower and upper Mesopotamia and northern Syria during the 3rd–7th centuries CE. 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. From that time, parts of the tribe settled in towns and villages along the Euphrates, while other parts remained nomadic and dwelt in the neighboring desert steppes. The Iyad played a significant role among the Arab tribes in the Fertile Crescent before the advent of Islam, as allies and opponents of the Sasanians and later allies of the Byzantine Empire. As the early Muslim conquests were underway, parts of the tribe in lower Mesopotamia embraced Islam, while those established in northern Syria and Upper Mesopotamia fled with the retreating Byzantine armies into Anatolia. They were expelled by Emperor Heraclius (r. 610–641) to Muslim territory after pressure by Caliph Umar (r. 634–644). Little is heard of the tribe afterward, though a number of Iyad tribesmen served as qadis (head judges) in different provinces of the Abbasid Caliphate in the 9th century and a family of the Iyad, that of Ibn Zuhr (d. 1162), grew prominent in Muslim Spain.