WWI Belgian Battle Site Ypres (5 letters) and Yser (4 letters) were two major sites of battle during World War I. Ypres was the site of three major battles, known as the First, Second, and Third Battles of Ypres, which took place between 1914 and 1918. The Yser River was the site of a major battle in October 1914, when Belgian forces attempted to stop the German advance into Belgium. Both sites saw heavy casualties and are remembered as important sites of WWI history.