Public murals are painted on walls by teams of untrained workers from the neighborhood under the direction of an artist, or they are created by a single artist with the backing of local citizens. By their nature, some murals are created without neighborhood sanction because they are designed to shock or surprise with their message.
The mural movement in the United States began in 1967 with William Walker and a group of African-American artists in Chicago. Walker and his group emulated the political and cultural murals painted in the 1920s by Orozco and other Mexican artists.
Walker and his team covered the wall of a Chicago building with a painting called "The Wall of Respect," using a theme of the accomplishments of black leaders in all fields. Its content was aimed at the people living in the surrounding neighborhoods.
William Walker's "Peace and Salvation, Wall of Understanding", created in 1970, is the wall mural on a four-story building at Locust and Orleans Streets in Chicago. It depicts gun battles between local gangs, marches for peace and a multi-racial group standing on a globe of the world.
The idea of public mural art has been picked up in other communities in the United States by Asian-Americans, Latinos and other groups who feel that muralism can help to affirm their cultural heritage.