The early development of the mammalian embryo leads to the formation of a structure composed by an outer layer of polarized cells surrounding an inner mass of nonpolarized cells. Experimental biology has shown that this organization results from changes in cell polarity, cell shape and intercellular contacts at the 8 and 16-cell stages. In order to examine how the physical properties of embryo cells (adhesion, cortical tension) influence the organization of the cells within the embryo, our team has developed a 3D mechanical model of the dividing early embryo, based on cellular Potts models. In this paper we will present the principles of our simulations, the methodology used and we will show that a very simple mechanical model can reproduce the main structural features (geometry, cell arrangement) of the mammalian embryo during its early developmental stages, up to the 16-cell stage.