Ypres was the site of an extraordinarily stable front line for several years during World War I. Defensive military technologies had improved while offensive technologies had failed to keep pace, so assaults inevitably gained little ground at the expense of enormous casualties. Thousands upon thousands of lives were sacrificed in order to eke out territorial gains of sometimes no more than a few hundred meters.
There were actually three battles at Ypres, of which the second and third are the most historically significant. The Second Battle of Ypres, in April 1915, saw the first use of poison gas during the conflict. The Third Battle of Ypres, July to November 1917, is also known as the Battle of Passchendaele for the ridge which was its military objective, and as the Battle of Mud for the swampy muck which the Allied soldiers had to cross. Many of those who fell off of the wooden duckboards drowned and disappeared into a glutinous mixture of ordnance-churned earth and heavy rain.
