But in the 7th century the Arabs suddenly acquired unity and world importance through Muhammad, the founder of Islam. His successors directed the desire for Holy War to the surrounding countries and thus promoted national unity and the Arabs' claim to power. The dinar became the universally recognised gold coin, and the dirhem the silver currency of the Islamic countries.

Mohammad
Muhammad was born in Mecca to poor parents in 570 and by marrying his employer became a rich merchant, familiar with the world as well as Judaism and Christianity. In the month of Ramadan in 610 the Angel Gabriel appeared to him, telling him to proclaim Allah, the only and invisible God. His wife believed in him, as did his cousin Ali. But the majority of the town's population rejected him. In 622 Muhammad fled to the second largest town, Medina. His escape, the Hegira, dates the beginning of the Moslem calendar. He died ten years later.


Caliphs
Muhammad's teachings were first recorded in writing in the Koran under his successors. The core of his creed is monotheism: "There is no God but Allah, and Muhammad is his prophet." But Muhammad failed to regulate his succession. As is customary with the Bedouins, the tribal leaders chose his father-in-law Abu Bekr to be the first Caliph (successor). This choice was a triumph for Abu Bekr's daughter, Aisha, Muhammad's 20-year-old widow, over his daughter Fatima, who was married to his cousin Ali. In 656 Ali was elected caliph after all, but in 661 was assassinated by Aisha's family, the Ummayyad dynasty. From this civil war a religious split developed which exists to this day: the supporters of the Ummayyad family revered not only the Koran but also the Sunna, the book of the first four caliphs, and thus called themselves Sunnis, while the Shiites, the party (in Arabic shia) of Ali, only recognised the Koran.


Spread
The triumphal advances of the Muslims can be explained by their willingness to die a martyr's death for their belief and by their modest requirements. Thus one Muslim offsets 100 believers in another faith. This pattern was valid for centuries. After the decline of the Roman Empire the Western world was in disarray. This made it possible for the Arab sphere of power to expand rapidly, along the coasts of North Africa to Spain via Gibraltar. While in Europe the Roman coinage system had fallen apart and was locally fragmented, the Arab world created its own coinage system. It thus effectively confronted the trade embargo imposed by Byzantium and built up a counterpole to the Byzantine solidus. For 750 years this stable coinage system was a cornerstone of the flourishing Arab economy and culture.