In Supremo Apostolatus

In 1839, Gregory XVI issued the apostolic letter In Supremo Apostolatus against the slave trade and chattel slavery, in which he wrote:

In the process of time, the fog of pagan superstition being more completely dissipated and the manners of barbarous people having been softened, thanks to Faith operating by Charity, it at last comes about that, since several centuries, there are no more slaves in the greater number of Christian nations. But - We say with profound sorrow - there were to be found afterwards among the Faithful men who, shamefully blinded by the desire of sordid gain, in lonely and distant countries, did not hesitate to reduce to slavery Indians, negroes and other wretched peoples, or else, by instituting or developing the trade in those who had been made slaves by others, to favour their unworthy practice. Certainly many Roman Pontiffs of glorious memory, Our Predecessors, did not fail, according to the duties of their charge, to blame severely this way of acting as dangerous for the spiritual welfare of those engaged in the traffic and a shame to the Christian name; they foresaw that as a result of this, the infidel peoples would be more and more strengthened in their hatred of the true Religion...

[W]e have judged that it belonged to Our pastoral solicitude to exert Ourselves to turn away the Faithful from the inhuman slave trade in Negroes and all other men...[D]esiring to remove such a shame from all the Christian nations, having fully reflected over the whole question and having taken the advice of many of Our Venerable Brothers the Cardinals of the Holy Roman Church, and walking in the footsteps of Our Predecessors, We warn and adjure earnestly in the Lord faithful Christians of every condition that no one in the future dare to vex anyone, despoil him of his possessions, reduce to servitude, or lend aid and favour to those who give themselves up to these practices, or exercise that inhuman traffic by which the Blacks, as if they were not men but rather animals, having been brought into servitude, in no matter what way, are, without any distinction, in contempt of the rights of justice and humanity, bought, sold, and devoted sometimes to the hardest labour...
 
We reprove, then, by virtue of Our Apostolic Authority, all the practices above mentioned as absolutely unworthy of the Christian name. By the same Authority We prohibit and strictly forbid any Ecclesiastic or lay person from presuming to defend as permissible this traffic in Blacks under no matter what pretext or excuse, or from publishing or teaching in any manner whatsoever, in public or privately, opinions contrary to what We have set forth in this Apostolic Letter.