As the conquests far beyond Arabia poured loot into the Holy Cities (Mecca and Medina), they became wealthy centres of a sophisticated Arabian culture; Medina became a centre for Qurʾānic study, the evolution of Islamic law, and historical record.Under the caliphs—Muhammad’s successors—Islam began to assume its characteristic shape; paradoxically, outside the cities it made little difference to Arabian life for centuries.Muhammad foiled Quraysh offensives and marched back to Mecca.After taking Mecca he became lord of the two sacred enclaves ( After Muhammad’s entry into Mecca the tribes linked with Quraysh came to negotiate with him and to accept Islam; this meant little more than giving up their local deities and worshiping Allah alone.Rejected by the Quraysh lords, Muhammad sought affiliation with other tribes; he was unsuccessful until he managed to negotiate a pact with the tribal chiefs of Muhammad’s men attacked a Quraysh caravan, thus breaking the vital security system established by the ʿAbd Manāf house, and hostilities broke out against his Meccan kinsmen.In Medina two problems confronted him—the necessity to enforce his role as arbiter and to raise supplies for his moves against Quraysh.The Prophet’s original simple mosque in Medina, already enlarged by the early caliphs, was rebuilt by the Umayyad al-Walīd (it has been much altered and restored since).

The Kaʿbah, through the additions of other cults, developed into a pantheon, the cult of other gods perhaps being linked with political agreements between Quraysh—worshipers of Allah—and the tribes.Tribes summoned to the banners of Islam launched a career of conquest that promised to satisfy the mandate of their new faith as well as the desire for booty and lands. Population movements of such magnitude affected all of Arabia; in Hadhramaut they possibly caused neglect of irrigation works, resulting in erosion of fertile lands.In Oman, too, when Arab tribes evicted the Persian ruling class, its complex irrigation system seems to have suffered severely.Sharīʿah (Islamic law), promoted often by the Prophet’s own descendants, developed in the urban centres; but outside them customary law persisted, sometimes diametrically opposed to Sharīʿah.In time the Hejaz and Yemen came to make notable contributions to Islamic culture, but Islam’s basically Arabian nature first shows in the early mosque, which resembles the pre-Islamic temple, and in the pilgrimage rites, little altered from paganism.ʿUthmān, however, the third caliph, was descended from both the Umayyah and Hāshim branches of ʿAbd Manāf.