The leader of the new invasion was a Mahdi, one of the numerous Saviours of the World who have carried death and destruction throughout Islam. His name was Ibn-Toumert, and he had travelled in Egypt, Syria and Spain, and made the pilgrimage to Mecca. Preaching the doctrine of a purified monotheism, he called his followers the Almohads or Unitarians, to distinguish them from the polytheistic Almoravids, whose heresies he denounced. He fortified the city of Tinmel in the Souss, and built there a mosque of which the ruins still exist. When he died, in 1128, he designated as his successor Abd-el-Moumen, the son of a potter, who had been his disciple.
Abd-el-Moumen carried on the campaign against the Almoravids. He fought them not only in Morocco but in Spain, taking Cadiz, Cordova, Granada as well as Tlemcen and Fez. In 1152 his African dominion reached from Tripoli to the Souss, and he had formed a disciplined army in which Christian mercenaries from France and Spain fought side by side with Berbers and Soudanese. This great captain was also a great administrator, and under his rule Africa was surveyed from the Souss to Barka, the country was policed, agriculture was protected, and the caravans journeyed safely over the trade-routes.
Abd-el-Moumen died in 1163 and was followed by his son, who, though he suffered reverses in Spain, was also a great ruler. He died in 1184, and his son, Yacoub-el-Mansour, avenged his father’s ill-success in Spain by the great victory of Alarcos and the conquest of Madrid. Yacoub-el-Mansour was the greatest of Moroccan Sultans. So far did his fame extend that the illustrious Saladin sent him presents and asked the help of his fleet. He was a builder as well as a fighter, and the noblest period of Arab art in Morocco and Spain coincides with his reign.
After his death, the Almohad empire followed the downward curve to which all Oriental rule seems destined. In Spain, the Berber forces were beaten in the great Christian victory of Las-Navas-de Tolosa, and in Morocco itself the first stirrings of the Beni-Merins (a new tribe from the Sahara) were preparing the way for a new dynasty.
The Beni-Merins or Merinids were nomads who ranged the desert between Biskra and the Tafilelt. It was not a religious upheaval that drove them to the conquest of Morocco. The demoralized Almohads called them in as mercenaries to defend their crumbling empire; and the Merinids came, drove out the Almohads, and replaced them.