Mecca and Medina were the regions where the new religion of Muhammed took root. Mecca had been attracting religious pilgrims to the Kaaba (a cubical granite house containing many idols, including a mysterious black meteorite). Kaaba was the focus of Muslim prayers since Prophet Muhammed favored the qibla (direction of prayers) to the Kaaba, Mecca. So, there were the sense of order in the radial orientation of mosques, tombs, and prayers toward qibla. Medina had the prototypical mosques as well and the basic idea of courtyard continued in here. In Medina, the Mosque of the Prophet resembled a small traders’ caravansary.
In the period of Islam religion, the earliest mosques took the place of the forum-basilica core of Roman cities. The first mosques provided simple architectural settings without apses, side chapels, ambulatories, crypts, baptisteries, or choirs. The first two generations of Islam demanded diverse structures to be transformed into mosques. The three most common plans to accomplish the idea, were the basilica with longitudinal aisles directed to the qibla, the transverse basilica with lateral exposure to the qibla wall, and the isotropic hypostyle hall.
The Umayyads settled in the Greco-Roman city of Damascus, Syria. They sponsored a brilliant urban culture here and those were partly based on the example of Byzantines in Constantinople. The Umayyad leadership constructed the exceptional central plan structure of the Dome of the Rock on the Temple Mount in Jerusalem to attract attention from other faiths. Dome of the Rock is like reminiscence of Late Roman and Byzantine tombs and baptisteries. The Dome of the Rock differed from most central-plan Christian churches in its use of two concentric ambulatories.
Mecca fell to the Umayyads a year after the completion of the dome of rock, and the realm of islam regained a sense of unity. Al-Walid I built three impressive mosques to celebrate the consolidation of empire. The first, he added mosaics and the first mihrab (a decorated niche indicating the qibla to Mecca) to enlarge the Mosque of Prophet in Medina. In ancient mosques, there was extendibility. The second, the Al-Aqsa Mosque, on the Temple Mount in Jerusalem. It has a hypostyle hall and it lined up with the southern portal of the Dome of the Rock. In the Mosques origins, it had a basilica plan. Al-Walid I’s third project, the Great Mosque of Damascus. It had a large lateral courtyard articulated with arcades on two levels. The structure had no windows and rose on eight Corinthian columns which are like spoils from the Roman temple. The structure, which had depictions of the Byzantine-style mosaics, also had a dome called maksura (literally closed space).
Both the Baghdad and Samarra appeared as the Abbasid capital at different times. Early Bagdad had two major cross-axial streets but instead of being lined with arcades, they were covered by vaults. The outer ring of round Baghdad’s blocks contained houses while the inner ring hosted military barracks and administrative buildings and the vast central void was for the palace and mosque. After Baghdad, Samarra became the new capital for Abbasid Empire. Samarra had the largest mosque in the world called the Great Mosque of Samarra built by Al Mutawakkil. It was covered roughly the same area as the Temple Mount in Jerusalem. It had hypostyle prayer hall, a minaret which reminds the ancient ziggurats of the region.
Reference: World Architecture: A Cross-Cultural History by Richar Ingersoll.