The Mystery of Celtic Wood refers to the apparent disappearance without trace of 71 men of the 10th Battalion of the 1st Australian Division during a diversionary attack on German positions in Celtic Wood, near Passchendaele in West Flanders, during the Battle of Poelcappelle (9 October 1917) in the First World War. Official Army reports of the action state that investigations have failed to account for the fate of 37 men of the 10th Battalion. German records contain no mention of the attack, which led to speculation that the men were massacred and buried in a mass grave. Visitors to the site today are still given this explanation by guides. Rumours persist that the men had simply walked into a mist and disappeared. Some investigators attribute the lack of record of the missing to confusion, mis-reporting and clerical error.