In a famous passage of his Geography, Strabo comments about a supposed peculiarity in the natural philosophy of the Stoic philosopher Posidonius of Apamea: ‘For there is much enquiry into causes in him [Posidonius], that is, “Aristotelising”, a thing which our School [the Stoics] sheers off from because of the concealment of causes’ (Strabo ii 3.8 = T 85 E-K). Yet, although the affinities between Posidonius’ aetiological project and Peripatetic scientific quest seem clear enough, scholarship has not investigated so far whether Posidonius’ interest in meteorology entailed the adoption of changes in the orthodox Stoic physics. This is the ultimate purpose of this article. I aim to show that Posidonius incorporated important Peripatetic concepts into Stoic cosmology. The article is divided into two sections. The first section presents the analysis of recent scholarship regarding the core concepts of the physics of the Early Stoa. In the second one, I examine in detail four fragments of Posidonius (F 84/97a, F 93a, F 229, F 219 EK) and identify the consistent modifications that he adopted: a finitist cosmological model, absolute directions in space guiding elemental motion, active and passive elements bearing mutually contrasting qualities, and heat as the efficient cause of meteorological phenomena.