Saturday's event was organized by a number of groups to protest a variety of Monsanto's practices, the St. Louis Post-Dispatch reported.
At a news conference held before the march, speakers criticized Monsanto for the alleged effects of some of their products and called for labeling of genetically modified food products, which the company manufactures.
Monsanto could not be reached for comment Saturday, the Post-Dispatch said, but issued a statement Friday before the protest.
"We believe we are making a contribution to improving agriculture by helping farmers produce more from their land while conserving natural resources such as water and energy," the statement reads.
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