A cylinder block for an internal combustion engine includes a network structure projecting from a sidewall thereof. The network structure is formed by a plurality of ribs including a first group of parallel ribs extending in a first diagonal direction with respect to an axis of a cylinder, a second group of parallel ribs extending in a second diagonal direction with respect to the axis of the cylinder, and a third group of parallel transverse ribs intersecting the diagonal ribs in such a way to form a triangular arrangement of ribs. The network structure further includes cylindrical portions in correspondence of the vertices of the triangular arrangement of ribs.