The defence on both sides consequently centred around the woods, villages, and numerous farms, which were converted into redoubts with concrete blockhouses and deep wire entanglements. The slightest bits of rising ground here played an important part, and were fiercely disputed. The crests which dominate the basin of Ypres were used as observation-posts--the lowering sky being usually unfavourable for aerial observation--while their counter-slopes masked the concentrations of troops for the attacks. It was therefore along the line of crests and around the fortified farms that the fighting reached its maximum of intensity. The principal military operations which took place in the vicinity of the town between October, 1914, and November, 1917, may be divided as follows:--First, a powerful German offensive--a counter-stroke to the battles of the Yser--then a very definite effort to take the town. The rôle of the Allied armies was at that time purely defensive. The second stage was marked by a British and Franco-British offensive, begun in the second half of 1916 and considerably developed during the summer and autumn of the following year. The object of these operations, which ended in November, 1917, was the clearing of Ypres. All the objectives were attained and the plains of Flanders were opened to the Allies. A final effort by the Germans in great strength to the south of the town was checked by the resistance of the Allies in April, 1918. In September and October, 1918, the enemy troops finally evacuated the country under pressure of the victorious Allied offensive. [Illustration: BRITISH SENTINEL ON NIGHT-DUTY IN FRONT OF THE RUINED CLOTH HALL] =THE GERMAN OFFENSIVE OF 1914= (October 29--November 15, 1914.) =Preliminary Operations= After the victory of the Marne, which drove the Germans north of the Aisne, began the operations known as "the Race to the Sea." Each side endeavoured to outpace the other, with the object of surrounding the enemy's marching wing. This remarkable "Race to the Sea"--a widely extended movement splendidly carried out by General Foch, and in which the Allied forces in their march towards the north constantly outstripped the enemy--might have been used as the starting-point for a grand Allied offensive against the German right, but the exhaustion of the Belgian army, after the terrible trials which it had just gone through in its retreat on the Yser--following on the fall of Antwerp--and the delays in the transport of the British troops from the Aisne front to the north, prevented the development of this offensive. It was therefore only possible for the Allied armies to fix their front and make it impregnable. The stages of this race to the sea and the fixation of the front took place between September 20 and October 23, 1914. =The Forces Engaged= (Oct. 1914)