The Roman church excommunicated Marcion around 144 CE and, by later report, returned the money he had donated. He did not simply disappear into obscurity afterward. Marcion organized a rival church with its own bishops, clergy and liturgy that spread across the Mediterranean and into the Near East, and evidence of Marcionite communities persists in some regions for centuries, well into the period when the wider church had settled its own canon partly in reaction to his.
That reaction was substantial. Justin Martyr wrote a treatise against him that survives only as a lost reference in later writers, Irenaeus addressed him at length in Against Heresies, and Tertullian devoted five books to Against Marcion, the most extensive rebuttal any single early Christian teacher received. The scale of the response is itself evidence of how seriously the wider church took the challenge: a bounded, edited canon and a flatly stated two God theology, argued by a wealthy and organized rival with his own clergy, forced the mainstream church to be explicit about claims it had previously left assumed.
Historians still disagree about how to classify him. Unlike the Gnostic teachers who read the Hebrew scriptures allegorically to extract a hidden meaning consistent with their own cosmology, Marcion read them literally and rejected them precisely because their literal sense struck him as unworthy of the true God, a distinction that has led some scholars, following the influential early twentieth century study by the German historian Adolf von Harnack, to treat Marcion less as a Gnostic than as a rigorous, if extreme, interpreter of Paul.