The French name (as used by the British) for the Flanders village of Passendale, a few kilometres east of Ieper (or Ypres in this context). Gave its name to the third battle of Ypres, 1917, in which the British and Empire forces launched an attack on the low ridge on which the village stands on the eastern side of the Ypres salient (in order to relieve the pressure further down the line following the mutinies in the French army after the appalling losses at Verdun and on the Chemin des Dames) in filthy weather which turned the normally merely hellish no-man's land into a swamp where soldiers could drown in mud without the intervention of the enemy. The battle became a byword for the worst that the Western Front had to offer and for any muddy disaster.
To get an idea of the scale of the battle and the nature of the ground, visit the huge Tyne Cot cemetery on the outskirts of Passendale. Unlike most of the many cemeteries that dot the line of the Western Front, this one is actually on the field of battle - the Cross of Remembrance is built on one of the German bunkers from which machine guns cut down troops struggling across the open slopes below. As well as seemingly countless graves, the cemetery contains one of the Ypres Salient's two monuments to the missing - the other being the Menin Gate - which lists something of the order of forty thousand names of soldiers lost in the area in the last two years of the war who have no known grave.