Both field observations and small-scale tests performed using shaking tables have shown that the distribution of lateral pressure of granular soils on rigid retaining walls during earthquakes does not have a linear shape. The purpose of this paper is to present a bilin-ear distribution, based on the Granular Mechanics, whose fundamental hypothesis is the transmission of stresses as networks of contact forces depending on the kinematics of the wall. As a result, a simple but general formula for the seismic lateral pressure is derived, that satisfies the pseudo-static equations of equilibrium and the boundary conditions, and comprises the distributions corresponding to the three elementary modes of wall movement: horizontal translation, rotation about the base, and rotation about the top. The juxtaposition of two or three distributions describes the more general cinematic conditions. Experimental data reported by several authors are used to prove the exactness of the theoretical lateral soil pressure.