This paper builds on Pierre Hadot’s analyses on the concept of the system of sciences in the ancient world. Starting from Hadot’s paper Les divisions des parties de la philosophie dans l’Antiquité, I aim to outline the limits and possibilities of his interpretation, based on the distinction between a Platonic pyramidal model of the system of sciences, a Stoic circular model, and a Neoplatonic pedagogical model. Reflecting on the Neoplatonic system of sciences elaborated by Proclus, it will be possible to see how it transcends the distinctions identified by Hadot. Here, in fact, not only does the pedagogical model find expression, but also the pyramidal and the circular model. In fact, Proclus has a spiral conception of the ontological structure of reality, given by the intertwining of circle and straight line. Such a conception, on the one hand, brings Proclus’ system of sciences closer to Platonic ontological hierarchization and, on the other hand, albeit with due differences related to a different conception of the divine, to the circular idea of the system of sciences that Hadot attributes to the Stoics.