In granular soils, stresses are transmitted by chains of contact forces from grain to grain. In this work, the average stresses are obtained based on two simplifying hypotheses: the linearization of the chains, and their association with bands of soil. In this way, the intersection of two conjugate bands gives rise to the definition of the basic element of the granular soil: the rhomboid, whose weight is resolved into two unitary forces of contact, which are added along an associated band to achieve the resultant force acting on the back face of a rigid retaining wall. As the kinematics of a wall rotating about its top requires that the lower grains rotate with respect to the upper grains of the backfill, the contact force against the wall follows a passive direction, whereas the conjugate force remains at the original direction, given by the at rest stress state. Because of the angle of the passive chain is greater than the failure angle, the lateral pressure becomes bilinear, with the maximum value near the top, in agreement with the experimental results of several authors. Hence, the lateral force is similar to that of Coulomb, but the point of application is higher.