Eleventh hour of the eleventh day of the eleventh month

from Writer's Almanac (American Public Media, Garrison Keillor):
Today is Veterans Day, honoring Americans who have served
their country in the armed forces. November 11 was originally
called Armistice Day, because it was on this day in 1918 that
the First World War came to an end. The armistice was signed
outside Paris at 6 a.m. in the railway carriage of Allied commander
Ferdinand Foch, and the cease-fire took effect five hours later: at
“the eleventh hour of the eleventh day of the eleventh month.”