Query: On what date did the Garde Nationale kill as many as fifty people on Champs de Mars?
Context: A law adopted by the new government on October 20, 1789 authorized the Garde Nationale to raise the red flag in the event of a riot, to signal that the Garde would imminently intervene. During a demonstration on the Champs de Mars on July 17, 1791, the Garde Nationale fired on the crowd, killed up to fifty people. The government was denounced by the more radical revolutionaries.