During al-Mansur's reign there was a rapprochement between that Persians and Arabs. Persian literature and scholarship became appreciated in the Islamic world.
Plan of the Round City of Baghdad, from www.faculty.fairfield.edu
Baghdad’s round plan found Persian precedents such as Ectabana, Hatra and Firouzabad. According to Manouchehr Saadat Noury (Persian Journal, 2005) two designers who were hired by Mansur to plan the city's design were two Iranians named Naubakht-e-Parsi, a former Persian Zoroastrian, and Mashallah-e-Assiri, a former Jew from Khorassan (a northeastern province in present-day Iran).
The city was designed with ash drawings onto the ground for al-Mansur to view prior to construction, which began that same year. By its completion in 766-7, it has been posited that the Round City measured 2000 meters in diameter.
It featured four main gates, equidistant from each other: the southwest gate was the Kufa Gate; the southeast was Basra; the Khurasan Gate extended to the northeast and the Damascus Gate to the northwest. The walls were constructed out of mud brick with reed supports, while the domes and vaults were composed in baked brick.
Manouchehr Saadat Noury