Sancho arrived late at the
Battle of Alarcos in 1195 and thus ruined good relations with
Alfonso VIII of Castile. The ensuing confrontation resulted in Sancho devastating
Soria and
Almazán and Alfonso accepted the Peace of Tarazona. Sancho made expeditions against
Murcia and
Andalusia, and, between 1198 and 1200, he campaigned in
Africa, probably in the service of the
Almohads, whose help he wanted against Castile. Taking advantage of his absence, Alfonso VIII of Castile and
Peter II of Aragon invaded Navarre, which lost the provinces of
Álava,
Guipúzcoa, and
Biscay to Castile. These conquests were subsequently confirmed by the Treaty of Guadalajara (1207). Sancho's leadership was decisive in the
Battle of Las Navas de Tolosa in the year 1212. In that engagement, the
Christian forces of Sancho, Alfonso,
Afonso II of Portugal, and
Peter II of Aragón allied to defeat the forces of
Almohad Caliph Muhammad al-Nasir. Sancho led a charge which broke through the bodyguard around the tent of the Caliph, who was slain. Supposedly the guards were slaves chained together to prevent any retreat or flight. In commemoration of this deed, the
coat of arms of Navarre bears an array of linked chains. Sancho's relations with the countries north of the
Pyrenees were notably better than his Castilian ones. Several Pyrenean counties declared themselves his vassals and he concluded treaties with
John, King of England, and with Peter II and
James I of Aragon. He signed a treaty with James in 1231, under which whoever survived the other would inherit the other's kingdom, but this treaty was never implemented. Sancho continued the construction of a new cathedral in Pamplona, which had been begun by his father and was finished by his successor. The construction of a certain
Gothic bridge over the
Ebro in
Tudela has also been attributed to him. == Succession ==