During centuries editors as well as compilers of St. Augustine have classified his work Contra Adversarium Legis et Prophetarum as anti-Manichean. Such a view is incorrect, inasmuch as several times St. Augustine acknowledges in his text not just his inability to identify the doctrinal affiliation of those he is trying to refute, but he also refuses to see his adversary as a Manichean. A recent proposal identifies the Adversarius as a Gnostic of that time. This proposal is developed by the author. Starting from the assumption that the Adversarius author was Gnostic, his affiliation to oriental gnosis, probably Mandaean, is demonstrated.