The North African religious leader Abdullah ibn Yasin (died 1059) was the founder and spiritual leader of the Moslem Almoravid movement.
Little is known of the life of Abdullah ibn Yasin until he stepped into North African history about 1050 as a missionary to the Sanhaja Berbers of the western Sahara. Himself a Berber, Ibn Yasin had been trained in the Maliki school of jurisprudence. He was living in the town of Nafis in the Moroccan High Atlas when he was invited by two Sanhaja leaders to instruct the Berber tribesmen of the Sahara in the true principles of Islam. Ibn Yasin proved to be a stern disciplinarian in the Maliki tradition, insisting that the Berbers abide by the letter of Moslem law in such matters as marriage, taxation, and punishment of criminals. Rather than give up their traditional practices, the Berbers denounced Ibn Yasin and his preaching.
Discouraged by this failure, Ibn Yasin withdrew with a small group of loyal followers to a Senegal island. There he established a ribat, or monastery-fortress, whose inhabitants (Arabic, al-Murabi-tun; English, Almoravids) gave their lives to religious instruction and devotion and to holy war against infidels. This combination of religious instruction, military discipline, and communal life directed from the ribat was as noteworthy for its success as his previous preaching was remarkable for its failure. In spite of the fact that the rules which Ibn Yasin imposed on his followers were strict and the corporal punishment which he personally inflicted for infractions, severe, his adherents soon numbered in the thousands, enough to subdue those very Berbers who had rejected his teachings. There is little doubt that the opportunity which Ibn Yasin gave the tribesmen for raiding and the taking of booty lent his doctrines an attraction which they had lacked at first.
About 1055 Ibn Yasin felt his forces were strong enough to undertake the conquest of urban centers in Morocco and Ghana. It is indicative of the increasing importance of warfare in the Almoravid movement that he turned over the leadership of the armies to one of his earliest followers, Yahya ibn Umar, retaining for himself the direction of spiritual and civil affairs. With this division of command, expeditions were sent against Sijilmasa in the north and Aoudaghost in the south.
The motives for attacking Sijilmasa were probably complex. Ostensibly, religion provided the occasion for the attack, inasmuch as a group of religious scholars had complained to Ibn Yasin that they were being persecuted by the ruler of the city. Tribal feelings were probably involved too, since the Berbers ruling the city belonged to the Zenata confederation while the Almoravids were Sanhaja. Finally, the fact that large amounts of booty were taken indicates the possibility that economic factors were involved. Northward expansion was continued in subsequent years into the cities of southern and central Morocco, in all of which Ibn Yasin attempted to impose the Maliki code of Islamic law. Thus, before his death in battle in 1059, he had created a base for the military expansion of the Almoravid empire into North Africa and Spain and laid down the guidelines by which it was to be governed.
In the absence of any detailed biographical study of Ibn Yasin see Henri Terrasse, History of Morocco (2 vols., 1949-1950; trans., 1 vol., 1952).