<P> Mexican muralism was the promotion of mural painting starting in the 1920s, generally with social and political messages as part of efforts to reunify the country under the post Mexican Revolution government . It was headed by "the big three" painters, Diego Rivera, José Clemente Orozco and David Alfaro Siqueiros . From the 1920s to about 1970s a large number of murals with nationalistic, social and political messages were created on public buildings, starting a tradition which continues to this day in Mexico and has had impact in other parts of the Americas, including the United States where it served as inspiration for the Chicano art movement . </P> <P> Mexico has had a tradition of painting murals, starting with the Olmec civilization in the pre Hispanic period and into the colonial period, with murals mostly painted to evangelize and reinforce Christian doctrine . The modern tradition has its roots in the 19th century, with this use of political and social themes . The first Mexican mural painter to use philosophical themes in his work was Juan Cordero in the mid 19th century . Although he did mostly work with religious themes such as the cupola of the Santa Teresa Church and other churches, he painted a secular mural at the request of Gabino Barreda at the Escuela Nacional Preparatoria (since disappeared). </P>

How did the mexican revolution affect the subject matter of mexican muralists