 The De opificio was often defined as a Jewish version of the Timaeus (Sterling 1993). In this treatise, Philo proclaims, against Aristotelianism and Stoicism, that God is the unique Creator both of the models for the world and of the world itself. That does not prevent him from drawing upon patterns elaborated in the somewhat confused but rich period at the end of the first century BCE. The evaluation of the most common model of cosmological creation in the De opificio, that of an active power acting on unqualified matter, is difficult since Philo seems to affirm that God created the world ex nihilo in some passages. It is probable that there was no significant difference between unqualified matter and pure void for him. God’s first task—though Philo refuses to admit the historicity of Creation (Runia 2001: 156–162)—was acting as architect to elaborate His project, i.e., to structure the intelligible world, conceived as the model of the corporeal one and established in the logos. The chief contents of the incorporeal cosmos were heaven, an invisible earth, air and void, water, spirit, and light. After the creation of the firmament and of the earth, on the fourth day God proceeded to order the heaven and to adorn it with splendid heavenly bodies. The explanation of this fourth day is especially interesting given the following elements: