 Sancho's brother, García, Bishop of Jaca, was perhaps too keenly aware of the reality of this hierarchy, for Sancho eventually came to suspect that his brother was planning to hand over Alquézar to Alfonso, "to subvert the kingdom of his brother and exalt the empire of Alfonso" in the words of a contemporary charter.According to the Islamic historian Ibn Khaldun, Alfonso VI "used the title of emperor, that is to say, king of kings".Alfonso was also the first Spanish monarch to use the term "imperium" to refer to an empire, the territory under the rule of an emperor, rather than as a synonym for power or authority.