But Ferdinand was at this time engaged in fighting his nephew, Alfonso IX. of Castile, and Affonso thought that he could take advantage of him. In 1167 he once more occupied Tuy and Limia, the two Gallician frontier cities, which he had formally surrendered by the Treaty of Zamora; and in 1169 he laid siege to Badajoz. This breach of treaty naturally incensed King Ferdinand, who collected a vast army, and besieged his father-in-law in his camp. The Spaniards were in every way successful; the Portuguese were everywhere defeated; their warrior monarch, now in advanced years, had his leg broken, and was forced to capitulate. Ferdinand used his victory with moderation; he remembered what great things Affonso had done for Christendom; and after two months’ captivity, he allowed the Portuguese king to return to his country on his surrendering the cities in Gallicia, and on the left bank of the Guadiana, which he had taken in violation of treaties. But the spirit of the old warrior was broken; he was never again able to mount a horse, and about the year 1172, he associated his son Sancho with him in the government of Portugal, to whom he gave the title of King, and assigned all the duties of war and the leadership of the Portuguese armies. Sancho was however a mere boy at this time, though he afterwards proved himself a worthy son of his father, and it was necessary for Affonso to take other measures against the Moors, who were now united under the Almohade caliph Yūsuf. He first promised the Knights Templars one-third of whatever they might conquer in the future, if they defended the Alemtejo. But the Templars were too weak in numbers to do much, and Yūsuf speedily reconquered the whole of the Alemtejo, and then laid siege to Santarem. Here however he was foiled; the defences had been strengthened with all the military skill known in the Middle Ages, and the city was well provisioned. Yūsuf was obliged to retire, and when he did so, Affonso, for the first time in his long career, made a truce with the infidels for seven years.