The Crescent and the Cross
The upheaval caused in the eleventh century by the invasion of the Maghreb by the wild Hillalian Arabs led to a period of war between Europe and Africa which for a time seriously interrupted trade. As the result of war and piracy numbers of Christian captives were constantly brought to the shores of Africa where they were sold as slaves. Among the first Christians to enter into formal treaties with the Muslims of Africa were the Norman kings of Sicily. All the country from El Mehedia in the east to the Atlantic in the west became subject to Abd el Mumen, their warrior Sultan, who had always disapproved of the presence of so many Christian galleys in African harbours. The death of Abd el Mumen in 1163 gave the Pisans an opportunity of reentering the field in which they had formerly been predominant, and of competing with their hated enemies the Genoese.