Photo: A colonnade of lofty arches surrounds the courtyard at the Prophet's Mosque in Medina, after Mecca the second holiest city of Islam.

After Muhammad  had preached publicly for more than a decade, the opposition to him reached such a high pitch that, fearful for their safety, he sent some
of his adherents to Ethiopia, where the Christian ruler extended protection to them, the memory of which has been cherished by Muslims ever since. But in Mecca the persecution worsened. Muhammad's  followers were harassed, abused, and even tortured. At last, therefore, Muhammad sent seventy of his followers off to the northern town of Yathrib, which was later to be renamed Medina ("The City"). Later, in the early fall of 622, he learned of a plot to murder him and, with his closest friend, Abu Bakr al-Siddiq, set off to join the emigrants.

In Mecca the plotters arrived at Muhammad's  home to find that his cousin, 'Ali, had taken his place in bed. Enraged, the Meccans set a price on Muhammad's  head and set off in pursuit. Muhammad  and Abu Bakr, however, had taken refuge in a cave where, as they hid from their pursuers, a spider spun its web across the cave's mouth. When they saw that the web was unbroken, the Meccans passed by and Muhammad and Abu Bakr went on to Medina, where they were joyously welcomed by a throng of Medinans as well as the Meccans who had gone ahead to prepare the way.

This was the Hijrah - anglicized as Hegira - usually, but inaccurately, translated as "Flight" - from which the Muslim era is dated. In fact, the Hijrah was not a flight but a carefully planned migration which marks not only a break in history - the beginning of the Islamic era - but also, for Muhammad and the Muslims, a new way of life. Henceforth, the organizational principle of the community was not to be mere blood kinship, but the greater brotherhood of all Muslims. The men who accompanied Muhammad on the Hijrah were called the Muhajirun - "those that made the Hijrah" or the "Emigrants" - while those in Medina who became Muslims were called the Ansar or "Helpers."

Muhammad  was well acquainted with the situation in Medina. Earlier, before the Hijrah, the city had sent envoys to Mecca asking Muhammad  to mediate a dispute between two powerful tribes. What the envoys saw and heard had impressed them and they had invited Muhammad  to settle in Medina. After the Hijrah, Muhammad's  exceptional qualities so impressed the Medinans that the rival tribes and their allies temporarily closed ranks as, on March 15, 624,
Muhammad  and his supporters moved against the pagans of Mecca.