The Battle of Verdun the longest and one of the costliest battles in human history began on this day in 1916. This World War I battle between the French and German armies lasted 303 days ending on December 18,1916. There were over 714,000 casualties and average of 70,000 a month. Those may be low estimates another estimate has casualties at 976,000. After all that non-sense the outcome was a French victory. The war would go on until November 1918.