 Apart from common interests, kings of Aragon and Castile were united by a formal bond of vassalage the former owed to the latter.Besides, on January 18, 1174, in Zaragoza Alfonso married Sancha, sister of the Castilian king.Another milestone in this alliance was the Treaty of Cazorla between the two kings in 1179, delineating zones of conquest in the south along the watershed of the rivers Júcar and Segura.