Medieval thinkers couldn’t help but borrow Manichaean themes when wrestling with questions of good and evil. Its stark dualism—light versus darkness, spirit versus matter—became a handy yardstick for labeling any doctrine that challenged orthodox Christian teachings. Augustine’s own dramatic shift from Manichaeism to Christianity didn’t erase its influence; instead, it armed him with intimate knowledge of heretical ideas and fueled his critiques in works like “City of God.”

When Cathars in southern France drew on similar dualistic concepts, church authorities were quick to slap the Manichaean label on them, whether or not they matched Mani’s original theology. During the Albigensian Crusade, accusing a group of “neo-Manichaeism” turned into a political weapon—branding opponents as enemies of the true faith. The Inquisition then wielded that same accusation like a double-edged sword, using it to justify interrogation, confiscation of property, even execution.

Beyond outright persecution, Manichaean thought subtly reshaped scholastic debates. Questions about the problem of evil, the origin of sin, and the material world’s corruptibility all carried the faint echo of Mani’s teachings. Thomas Aquinas and his peers regularly crafted rebuttals aimed at dualistic worldviews, inadvertently refining their own arguments on creation, free will, and God’s sovereignty.

Fast-forward to today: new Manichaean manuscripts unearthed along the Silk Road are turning heads at universities from Oxford to Beijing, proving that this once-condemned faith still has surprises in store. Modern interfaith dialogues over religious pluralism and spiritual dualities frequently trip over terms first popularized by Manichaeism. That enduring footprint—splashed across medieval heresy trials and into twenty-first-century scholarship—shows how a religion thought vanquished can leave a legacy more resilient than anyone might have expected.