island named Ribat, on the upper Niger, where he collected adherents round him and promulgated his puritanical reforms. Gradually Ibn Yaṣin’s influence extended over the whole Lamta or Lemtuna tribe, and he urged these Berbers towards the conversion of Senegambia. It was mainly through his influence that the Berbers were carried by their conquests into Senegambia and Nigeria. Then he led them (about 1050) north-west across the Sahara Desert; and they conquered Morocco, and from thence invaded Muhammadan Spain. By this time Ibn Yaṣin, the teacher, was dead, but the warrior chief of the Lamta tribe—Yussuf-bin-Tashfin—had become sovereign of Morocco and Spain, and had assumed the title of Amir-al-Mumenin[37]. A hundred years later another Berber Mahdi arose in the person of Ibn Tumert, who was “run” by Abd-al-Mumin of Tlemsan (West Algeria), and whose fighting force was the great Berber tribe of the Masmuda from the High Atlas Mountains. The programme was the same—to start with puritanical reform, afterwards degenerating rapidly into mere lust of conquest. This small sect known by us as the “Almohades” (from Al-Muāḥadim or Muaḥidūn, meaning “(Disciples of) the Unity of God[38]”) attacked the decaying power of the Almoravides. Ibn Tumert—an exact parallel of all the Mahdis—died early in the struggle, but was succeeded as “Khalifa” by his warlike lieutenant, Abd-al-Mumin, who pursued his conquests until he had brought under his power all North Africa and Muhammadan Spain, and had founded the greatest Berber empire that ever existed. Concurrently, however, with the sway of his overlordship, the Ziri and Hamadi dynasties of Berber sultans continued to exist at Tunis and in eastern Algeria. After ruling for a century the Almohade empire broke up, and was succeeded by independent Berber rulers in Tunis and Tripoli (the Hafsides), in Algeria (the Abd-al-Wadite or Zeyanite kings of Tlemsan), and in Morocco (the Marinide or Beni-Marin). Remarkable among these was the Hafs dynasty, which governed Tunis and part of Tripoli for 300 years, and proved the most beneficent of all Muhammadan rulers in North Africa. Abu Muhammad Hafsi was a Berber governor of Tunis under one of the last of the Almohade emperors, and eventually became the independent sovereign of Tunisia. The Almohade rulers, towards the end of the 12th century, had transported most of the turbulent Arabs of southern and central Tunisia to Morocco, where for the first time the Arabs began to form an appreciable element in the population. About this time Kurdish and Turkish mercenaries began to find employment in Tunisia and in Tripoli under chiefs who rebelled against the Almohade empire. During the period between 1250 and 1500 the Moorish civilization, art, architecture, letters, and industries reached their highest