Then, arose the question of progressing towards the East and towards the North. The works of extension were commenced, but it was soon realised what a great effort and incessant sacrifice such an enterprise would demand, that about Mai 1915 the bridge-head was brought back to its former line. During the course of the war, the evolution of fighting methods altered and likewise the mission of the advanced positions and the effective forces of the garrisons which held them. For this reason, when the bridge-head of kilometer 19.500 was created, and which had to resist to the utmost, it required more than one battalion to guard it; and in 1918, a few posts of section or squad sufficed, the mission of the advanced ones having simply become at this place, for watching purposes in case of a defensive, or kick off in the case of an offensive. To give one an exact idea of the enormous effort that the bridge-head of the kilometer 19 cost, one needed to see the development and extension it had taken in May 1915 and be equally penetrated with the idea, that all the work had been done at the price of heavy losses, although it had been done by night, under the bullets and shrapnells, in bad weather and often with reduced means. This bridge-head contributed greatly to maintain an offensive spirit in the minds of the infantrymen, it served also as a base to many patrols towards the enemy’s organizations and notably to a famous raid on the castle of kilometer 19 on the night of the 28^{th} to the 29^{th} of October 1917, which was a brilliant success, led by Captain Dendal, who brought back materials and prisoners. Several times the Germans tried to rush the bridge-head of kilometer 19, but without any result whatever. And then during the offensive of September 1918, it served as a starting trench to the troops of the Belgian 4^{th} division, for the victorious assault which ended by the liberation of Dixmude. 21.—Observation-post near the Church of Clercken. Clercken Ridge was very precious to the enemy to whom it gave the opportunity to establish a lot of natural observation-posts which had not the vulnerability of the confined kite balloons and which assured more stability to the observation. Many of these posts were destroyed during the war, especially by the destructive fires which preceded the great offensive in Flanders on the 28^{th} of September 1918. Others, such as the mill of Clercken, are already rebuilt, so offer no longer any historical interest. [Illustration: German observation-post near the church of Clercken. Sketch showing the directions of the villages seen from this observation-post. ]