In Reconquista Spain, a barely united state turned its anxieties inward with anti-Semitic laws on blood purity among converts from Judaism and Islam. The same insecure state turned outward to conquer Mexico, where Franciscans spent fifty years recording Aztec human sacrifice in codices and color drawings. Castilians and Aztecs alike marked their external bounds and internal bonds with blood. Ethnicizing ideas of blood purity crossed the Atlantic to ruddy Christian perceptions of Mesoamerican sacrifice. Two blood-obsessed cultures met to reveal disturbing resonances in Christian blood language. Uses Sircoff on limpieza de sangre and Timothy Radcliffe on cultic irony in Hebrews.