 The corpus of the "PGM" were not based on an ancient archive, but rather are a modern collection that has been added to over time.The unclear circumstances of each text's production, over a span of centuries, have therefore occasioned some debate.Betz, the English translator of the "PGM", claims that the texts form a fraction of the "magical books" that must have existed in antiquity, and considers them a form of "underground literature" subject to book-burnings at the time.