[3][4] After having suffered a great defeat with his own army at Alarcos against the Almohads in 1195,[5] he led the coalition of Christian princes and foreign crusaders who broke the power of the Almohads in the Battle of Las Navas de Tolosa in 1212, an event which marked the arrival of a tide of Christian supremacy on the Iberian Peninsula.

[6] His reign saw the domination of Castile over León and, by his alliance with Aragon, he drew those two spheres of Christian Iberia into close connection.

This division set the stage for conflict in the family until the kingdoms were re-united by Alfonso VIII's grandson, Ferdinand III of Castile.

The devotion of a squire of his household, who carried him on the pommel of his saddle to the stronghold of San Esteban de Gormaz, saved him from falling into the hands of the contending factions.

In 1159 the young Alfonso was put briefly in the custody of García Garcés de Aza, who was not wealthy enough to support him.

[9] During the regency, his uncle Sancho VI of Navarre took advantage of the chaos and the king's minority to seize lands along the border, including much of La Rioja.

In April 1188, they agreed on a treaty in Seligenstadt, which made clear that she was the heiress of Castile after any sons of Alfonso and that Conrad would only co-rule as her spouse.

In July 1188, Alfonso convened his court in Carrión de los Condes to allow the nobles to review and ratify the treaty.

[12] The annulment of this marriage by the pope drove the younger Alfonso to again attack his cousin in 1204, but treaties made in 1205, 1207, and 1209 each forced him to concede further territories and rights.

[15] Around 1200 when his brother in law John was on the English throne, Alfonso began to claim that Gascony was part of Eleanor's dowry, though there was nothing in the marriage treaty to indicate this.

Castilians under Alfonso, Aragonese and Catalans under Peter II, Navarrese under Sancho VII, and Franks under the archbishop of Narbonne, Arnaud Amalric, all flocked to the effort.

[21] With Eleanor of England,[22] Alfonso had 11 children:[23] Through his daughters, Berengaria and Blanche, he was the grandfather of two monarchs who became saints of the Roman Church.