The British were forced to lay siege to the place. The operations, begun on July 3, 1916, lasted till October. On July 7, the British carried the greater part of the Leipzig Redoubt (Hill 141), a powerful stronghold which protected Thiepval from the south, and consisting of a system of small blockhouses connected up by a network of trenches. A wide breach opened by the artillery, enabled the troops to gain a footing in the position and conquer it trench by trench. Throughout the months of July and August the struggle went on, with unabated fury, around the fortress. Fighting with grenades, the British advanced inch by inch, so to speak, and eventually gained a footing in the village, to the east and south. Each advance was immediately followed by a violent counter-attack, as the Germans looked on Thiepval as the key of the Bapaume position. On August 26, in particular, the Prussian Guard attacked the British lines of the Leipzig Salient. The struggle was one of "giants." After furious hand-to-hand fighting, the Wiltshire and Worcestershire Regiments broke the assaulting waves and inflicted "frightful" losses on the enemy. At no point were the British positions pierced; on the contrary, progress continued to the south and south-east. On September 15, the Australians captured Mouquet Farm which, on the right, formed the advance-bastion of the fortress. Thiepval was now completely surrounded from south to east, and after a last artillery preparation of extreme violence, the final assault was made. At 12.30 a.m., on September 25, the Canadians attacked the castle and southern part of the village, one of the strongholds of the fortress. After fierce fighting, which lasted two hours, they captured the defence-works, being helped by the tanks which, crushing everything before them, destroyed the nests of machine-guns hidden on all sides. The battle went on throughout the following day in the village, the cellars of which were connected with one another and fortified, forming so many nests of machine-guns. Detachments of Wurtembergers who, by means of underground passages, had slipped behind the Canadians, were either exterminated or captured. In the evening, the cemetery, which formed the centre of resistance in the northern part of the village, was carried. Thiepval was thus entirely conquered, as well as the Zollern Redoubt, which dominates it on the east. The British followed up their success by attacking the fortified positions to the north and north-east, on the line of hills which dominate the Valley of the Ancre near Grandcourt, where the Germans had also made formidable entrenchments, comprising the Stuff Redoubt (to the north-east), the Schwaben Redoubt (to the north), and between the two, astride of the Thiepval-Grandcourt road (G.C. 151), the Hesse Trench. Behind these, in the direction of Grandcourt, the Shiff and Regina Trenches, likewise powerfully organised, formed a second line of entrenchments.