The front line around Ypres had changed little since the end of the Second Battle of Ypres ( May 1915). The British held the city and the Germans held the high ground of the Messines–Wytschaete Ridge to the south, the lower ridges to the east and the flat ground to the north. High ground is relative; Passchendaele is on a ridge about above the surrounding plains. The Gheluvelt plateau is about above the vicinity and Wytschaete is about higher than the plain; control of the ground was vital for artillery observation. The Ypres front was a salient bulging into the German lines and was overlooked by German artillery observers on the higher ground. The British had little ground observation of the German rear areas and valleys east of the ridges.