All these advances, with their accompanying and {7} ever-extending bombardments, had been like those multiplied causes, each small in itself, which eventually loosen and start a great landslide. The effect must undoubtedly have been begun some weeks before when the Germans perceived that they could no longer hold on, and favoured by wind, rain, and fog, started their rearward movement to the great permanent second line, the exact position of which was still vague to the Allies. Upon February 25 the whole German front caved in for a depth of three miles both north and south of the Ancre. Wading through seas of mud Gough's infantry occupied Serre, Pys, Miraumont, Eaucourt, Warlencourt, and all the ground for eleven miles from Gomiecourt in the north to Gueudecourt in the south. On February 28 Gomiecourt itself had been occupied by the North Country troops of the Thirty-first Division, while Puisieux and Thilloy had also been added to the British line. The advance was not unopposed. The battle-patrols continually extended to attack some trench of snipers or nest of machine-guns. Mined roads and all manner of obstructions impeded the onward flow of the army. The retreat was orderly and skilful, and the pursuit was necessarily slow and wary. By a pleasing coincidence the Thirty-first Division, which occupied Serre, was the same brave North Country Division which had lost so heavily upon July 1 and November 13 on the same front. On entering the village they actually found the bodies of some of their own brave comrades who had got as far forward seven months before. [Sidenote: March]