In the late Roman empire, the papacy’s endorsement of marriage as a divine institution was already explicita. From the mid-fifth century, fundamental importance was attached to the signification by marriage of Christ’s union of the Church, a value shaping the social practice of marriage, underpinning the creation in Roman Catholicism of a marriage system unique in the history of literate societies, one which banned both polygamy and divorce. More flexible laws limited marriage within the “forbidden degrees” of relationship. The aim was to foster social cohesion. These rules could be changed, or dispensed with, in individual cases. Marriage was made by consent, and only from the Council of Trent was the presence of a priest required. Christianity in general and papal law in particular slowly transformed the relationship between slavery and marriage.