In 1904 when the Olympic Games were held at Francis Field, and in 1984, 1996, and 2004 as the part of the torch relay leading up to the Olympics. 

For more information see:

WU Record, July 5, 1984, page 1;

Washington University Magazine Summer 1996, page 14 (http://digitalcommons.wustl.edu/ad_wumag/136);

Washington University Magazine, Fall 2004, page 8 (http://digitalcommons.wustl.edu/ad_wumag/169)