This article explores the representation of royal power in the tenth-century county of Castile by contrasting the low degrees of effective royal agency within the county with a dominant charter-writing tradition that coupled king and count in the synchronisms of the dating clauses. The components of the Castilian charter corpus are broken down and compared to other areas in northern Iberia, in order to suggest that, rather than a mere regional charter-writing tradition, this practice reflects a widespread political culture that sought to legitimize the counts' unitary leadership of Castile by reference to a prestigious yet distant royal figure.