In the sixth century, the city of Mecca rose to prominence in the Arabian peninsula because of the popularity of its religious shrine, the Ka’ba, and its trade with the Byzantine and Persian Empires. The Prophet Muhammad (ca. 570–632) began his adult life working Mecca’s caravans, but on turning forty he began to have revelations that formed the basis for the Qur’an. In 622, Muhammad was forced out of Mecca and led his followers to Medina, where he settled disputes between Jewish merchant groups and eventually became the leader of the city. Muhammad later captured the city of Mecca and united the nomadic tribes of the Arabian peninsula. Under Muhammad’s successors, the caliphs, Islamic armies conquered the Middle East, North Africa, Spain, and portions of northern India. In so doing, the Muslims encountered Jews and Christians — honored as fellow “people of the book” — as well as polytheists, whom they persecuted. During the Umayyad (661–750) and the Abbasid (750–1258) Dynasties, the Islamic caliphate dominated the world in economic activity, scientific development, and culture.