The photo below was taken on Wednesday, August 28, 1968, as the demonstrators converged around the Poor People's Campaign mule train and approached Michigan Avenue.
Source:
Daniel Walker, "How the City Prepared," Rights in Conflict: Chicago's 7 Brutal Days, a report submitted by Daniel Walker, Director of the Chicago Study Team, to the National Commission on the Causes and Prevention of Violence (New York: Grosset & Dunlap, Publishers, 1968), A-51.