With the spread of Islam in the early middle ages, Arabic became the lingua franca of the empire ruled by Muslims, which was populated also by large numbers of Jews and Christians. Islamic rule provided the umbrella under which various cultural traditions could merge to form a new, imperial culture, which comprised all peoples of various faiths and different ethnic backgrounds living within the dār al-Islām. One of the characteristic features of early Abbasid culture is the prominence of intellectual figures of non-Arab background. Important contributions were made by translators from Pahlavi, but also by East Syrian Christians. The most famous institution associated with the transmission and cultivation of learning is the House of Wisdom (bayt al-ḥikma). The Abbasid court stimulated numerous translations from Greek and Persian into Arabic. The translation movement received its impetus from the Abbasid power centre, drawing non-Muslims into its orbit, who participated in and contributed to the emergence of an Islamic culture, not only by translating texts into Arabic, but also by stimulating interfaith dialogues, which contributed to the emergence of an Islamic apologetic theology (kalām). The imperial culture of early Abbasid Iraq was nurtured and shaped by a synthesis of different traditions achieved by cultural brokers at the imperial centre of the Islamic caliphate.