Pope Leo The Great Described the Wickedness Of The Manichaeans

Jan 14, 2026

Manichaeans were radical dualists, believing in two rival supreme principles and many associated heresies.

“Manichaeism is a religion founded by the Persian Mani in the latter half of the third century. It purported to be the true synthesis of all the religious systems then known, and actually consisted of Zoroastrian Dualism, Babylonian folklore, Buddhist ethics, and some small and superficial, additions of Christian elements. As the theory of two eternal principles, good and evil, is predominant in this fusion of ideas and gives color to the whole, Manichaeism is classified as a form of religious Dualism. It spread with extraordinary rapidity in both East and West and maintained a sporadic and intermittent existence in the West (Africa, Spain, France, North Italy, the Balkans) for a thousand years, but it flourished mainly in the land of its birth, (Mesopotamia, Babylonia, Turkestan) and even further East in Northern India, Western China, and Tibet, where, c. A.D. 1000, the bulk of the population professed its tenets and where it died out at an uncertain date.” (J. Arendzen, “Manichaeism”, The Catholic Encyclopedia, 1910)

Some of the Manichaeans engaged in perverse rites. They were a significant problem at the time of Pope St. Leo the Great. He described their wickedness and told Catholics to avoid all friendship with them.

Pope St. Leo the Great, Sermon 16, Dec. 12, 443: “But while he [the Devil] retains this ever-varying supremacy over all the heresies, yet he has built his citadel upon the madness of the Manichaeans, and found in them the most spacious court in which to strut and boast himself: for there he possesses not one form of misbelief only, but a general compound of all errors and ungodliness. For all that is idolatrous in the heathen, all that is blind in carnal Jews, all that is unlawful in the secrets of the magic art, all finally that is profane and blasphemous in all the heresies is gathered together with all manner of filth in these men as if in a cesspool. And hence it is too long a matter to describe all their ungodly acts: for the number of the charges against them exceeds my supply of words… in that sect no modesty, no sense of honor, no chastity whatever is found: for their law is falsehood, their religion the devil, their sacrifice immorality. And so, dearly beloved, renounce all friendship with these men who are utterly abominable and pestilential, and whom disturbances in other districts have brought in great numbers to the city…”