A lateral periodic submicrometer potential in one direction superimposed on a two- dimensional electron gas (2DEG) lifts the degeneracy of the Landau levels (LLs) and leads to modulation broadened Landau bands. Due to the new band structure, singularities in the density of states (DOS) are expected which should result in a double peaked structure of the LLs (Van Hove singularities). Increasing the modulation amplitude of the periodic potential we observe a splitting of the Shubnikov-de Haas (SdH) maxima in magnetoresistance measurements which we believe to be the first observation of van Hove singularities in such modulated systems. In addition we report magnetotransport experiments in a weak two-dimensional periodic potential