Original: In 1212 Muhammad III , '' al-Nasir '' ( 1199 -- 1214 ) , the successor of al-Mansur , after an initially successful advance north , was defeated by an alliance of the four Christian princes of Castile , Aragón , Kingdom of Navarre and Portugal , at the Battle of Las Navas de Tolosa in the Sierra Morena .
Simplified: But by 1212 Muhammad III , '' al-Nasir '' ( 1199 -- 1214 ) was defeated by an alliance of the four Christian princes of Castile , Aragón , Kingdom of Navarre and Portugal , at the Battle of Las Navas de Tolosa in the Sierra Morena .