This study examines the correspondences between reconquest, repopulation and the acceptance of Castilian as an official written language. While recent research has focused on how the Castilian monarchy sought to invent written Castilian as a sacred script comparable to Latin, Arabic and Hebrew, or simply as a prestigilas language of culture, my reading of the Siete Partidas is more concerned with vernacular writing as a regulatory practice and vernacular writings as administrative tools sanctioned by the Crown to facilitate the socio-juridical control of repopulated spaces and peoples. Ultimately, the practical demands of territorial conquest were more critical to the acceptance of Spanish writing than any purely cultural concerns the Crown may have had.