A stone from a bridge over the Marne River in France. In late May 1918, French and American forces used the bridge to repel the last big German offensive of World War I as they tried to cross the last natural barrier protecting Paris. On May 30, American machine gunners blocked the advance; on June 1, French engineers blew up the bridge. The Legion, of course, was formed in 1919.
The stone was presented to the Legion by the mayor of nearby Château-Thierry in August 1920. It is currently on loan to, and on display at, the Indiana War Memorial near National Headquarters in Indianapolis. April 6 marks the anniversary of the date in 1917 when the United States formally declared war on Germany. See the stone in the virtual tour here.