My dissertation explores circulations of knowledge about African Christianity within the Iberian Atlantic during the first century and a half of Iberian expansion from 1509-1640. In the sixteenth century, hundreds (if not thousands) of free Afro-Iberians, some of them first generation Africans (manumitted slaves) acquired royal permits to embark in fleets to cross the ocean as vassals of the crown, that is, as Old Christians. The idea of "Christian Ethiopia" allowed crown bureaucrats, free blacks, and slaves to agree that Africans were entitled to claim an "Old" Christian status. Debates about "Christian Ethiopia" circulated amongst European missionaries, the Spanish crown, religious authorities, black individuals, and black religious brotherhoods in key urban spaces. The idea of Ethiopia came to life in books penned by learned clerics and the ambitious plans of universal monarchs trying to justify planetary expansion. But is also came alive in everyday lives of free blacks who participated in the activities of black religious brotherhoods that venerated "Ethiopian" saints in the port cities that constituted the Iberian Atlantic between 1500 and 1650 (and beyond). These brotherhoods created the conditions for black literacy and a black learned republic. I explore how itinerant free blacks served as cultural intermediaries, connecting urban black communities across the Atlantic and disseminating ideas about Christian Ethiopia and African Christianity, particularly in and between Seville (Spain), Veracruz (in present day Mexico), and Cartagena de Indias (in present day Colombia). My dissertation challenges a long-standing historiographical tradition that claims that Africans were considered the ultimate outsiders in the Spanish Monarchy, members of stained human lineages, and inassimilable converts.