Porphyry's Witness of the Marcionite Interpretation of Galatians

That impious man Porphyry from Batanea did not comprehend any of this (i.e. the 'correct' interpretation of Galatians). In the first book of his treatise against us [Christians], he alleged that Peter had been rebuked by Paul because he did not walk uprightly as he spread the Gospel. His intention was to charge Peter with error and Paul with impudence and to implicate the entire community [of Christians] in the lie of fabricated teaching on the grounds that the leaders of the churches disagreed amongst themselves. [Jerome, Commentary on Galatians, Introduction, Cain translation p.60]

The reference to Batanea is interesting too because it also happens to be the place from which the early Jewish Christian sects who used 'the Gospel according to the Hebrews' and related texts - no less than the Marcionites - were supposed to have existed in great number.