Among the hallmarks of historiographical seriousness is a concern to avoid over-generalization. In that spirit, since I have made quasi-polemical references to Augustine and Augustinianism in broad-brush sketches of the history of notions of subjectivity, it seems right to pause for a few caveats.
Augustine is the main early source in the Western tradition for a specific notion of mental interiority. However, at the very beginning there is a surprising twist. At least, it is surprising for us moderns conditioned by Descartes and Locke. For it turns out that for Augustine, when one looks within to the inner man, what one finds is the opposite of something private.
For Augustine, the inner man participates in a community of the spirit, and interiority opens out into universality. The inner man is a source of a kind of integrity more than individuality. It is rather our view of the external world that is the locus of what we might call subjective particularity. The idea that what is inner is universal puts Augustine much closer to Plotinus than to Descartes in this way. The inner man is not a modern ego. Augustine fused notions of mind and personality, but again, his variant of the notion of personality had more to do with trinitarian theology than with individuality. Even the meaning of his early strong voluntarism is modified by this.
Among the early Christian fathers, Augustine was among the most philosophical. According to his own testimony in the Confessions, his reading of Plotinus was a spiritual event second only to his conversion to Christianity, and remained important after his conversion. As much as he emphasized faith, he also emphasized seeking understanding. He clearly acknowledged a degree of bilateral accommodation of faith and reason, for instance in his writings on the interpretation of scripture.
It should also be noted that many of the later theologians I broadly characterize as Augustinian developed sophisticated hybrid positions on various philosophical issues, however much I might criticize, e.g., their voluntarism or their anti-Aristotelianism couched in Aristotelian vocabulary. (See also Ricoeur on Augustine on Time; Nature and Justice in Augustine; Mind Without Mentalism; Subject; Freedom and Free Will; God and the Soul.)