A serious yet unstudied consequence of the Christian-Muslim conflict in medieval Spain was the capture and enslavement of soldiers and civilians. Men, women, and children who were seized on raids, taken in battle, or pirated off ships were regarded by their captors as booty, to be used as slaves or to be sold for profit. Since warfare in twelfth-century Spain pitted Christians against Muslims, the usual prohibitions against enslavement of coreligionists clearly did not apply.' For Muslims and Christians alike, capture meant a life of slavery. Christian chronicles of this era are replete with stories of captives taken off to be sold in the slave markets of al-Andalus in southern Spain or, even worse, in those of North Africa.2 Some of these slaves, however, were able to regain their freedom through redemption that is, to purchase their liberty by paying a ransom. Since the ransom price frequently exceeded what could be gained in the slave auctions, redemption became an attractive option to both captor and captive. Ransoming is probably as old as slavery, and in Spain prior to the twelfth century there are numerous instances of kings ransoming their soldiers and parents their sons.3 It was not until the twelfth century, however, that the practice of redemption became institutionalized. This attempt at systematization coincided with the extension of Leon-Castile into the trans-Tagus and of Aragon into the middle Ebro valley at the end of the eleventh and the beginning of the twelfth centuries. Here, at the peninsula's center, new Christian communities were planted on what would be a shifting and volatile frontier with the fierce Murabits (or Almoravids) and Muwahhids (or Almohads), those Berbers of North Africa who had absorbed the fragments of the old Islamic caliphate in Spain. Thus, until Islam's decisive defeat at Las Navas de Tolosa in 1212 and the transfer of the conflict to Andalusia and Murcia, there existed in central Spain a Muslim-Christian frontier across which the military forces of both sides attacked and raided.4