ridge had been a mixture of meadow and fields, with high hedgerows dotted with trees, cut by streams and ditches emptying into canals. The main road to Ypres from Poperinge to Vlamertinge is in a defile, easily observed from the ridge. Prelude German defensive preparations Fortification The 4th Army (General Friedrich Bertram Sixt von Armin) was responsible for defence of the Western Front from Lille to the North Sea, which included the Ypres Salient. In early 1917, German corps had been renamed based on a corps headquarters, with fresh divisions coming under command as tired ones were withdrawn rather than the previous permanent establishment of divisions. The IX Reserve Corps became and held a front south of the Menin road with three divisions holding the front line () and three (specially trained counter-attack) divisions in reserve. The III Bavarian Corps was renamed Gruppe (group) Ypres and held of front, from the Menin road to the Gheluvelt plateau and Pilckem to the north, with three front divisions and two divisions. The divisions were kept out of sight behind the Menin and Passchendaele ridges and further back were four more divisions; beyond were another two divisions in army group reserve. The Germans were apprehensive of a British attempt to exploit the victory over at Messines, with an advance to the Tower Hamlets (Bassevillebeek) spur beyond the north end of the ridge. Since early 1917, there had been three German defensive positions behind the front line. The ran from Bixschoote in the north, behind Pilckem Ridge and south across the Gheluvelt Plateau. The began at Langemarck, ran south to Gravenstafel then crossed the Gheluvelt Plateau to Zandvoorde, east of Messines Ridge. The (Flanders Position) had been built earlier in the year, along Passchendaele Ridge, south across Gheluvelt Plateau behind Polygon Wood, in front of Becelaere, across the Menin road and south to the Lys (Leie) river. Because of the flat ground and high water table hundreds of pillboxes and blockhouses rather than deep dugouts, had been built above ground and camouflaged with mud and turf. The many stone farmhouses dotted around had also been fortified; from two to forty men could be accommodated in the concrete and steel shelters, immune to anything smaller than a hit by an 8-inch shell. On 9 June, Rupprecht proposed withdrawing to the in the area east of Messines; construction of defences began but were terminated on 14