The British continued to close in around Lens from three directions, their progress being slow owing to the stubborn attacks made by German rear guards and the fierce fire of cunningly placed machine guns. Field Marshal Haig's chief purpose in advancing on Lens was to turn La Bassee from the south. La Bassee and Lens form the principal outworks of Lille, which is the key to the whole German position in Flanders. If the British succeeded in capturing these two places, Lille would be seriously threatened. On the 15th the British continued to gain ground in the direction of St. Quentin and east and north of Gricourt, to the north of the city. In the morning the Germans delivered a powerful attack over a front of six miles against the new British position, which extended from Hermies to Noreuil. In the face of a terrific fire from British artillery they forged ahead, but lost so many men that they were at last forced to retreat, gaining no advantage except at Lagnicourt village, to one part of which they clung tenaciously. Immediately the British organized a counterattack, which was carried out with dash and spirit. The Germans were driven out of the village and 300 prisoners were taken. Some 1,500 dead were left in front of the British positions. April 16, 1917, was a day of glory for French arms, when General Nivelle launched a great attack on a front of about twenty-five miles between Soissons and Rheims. The French were everywhere successful, capturing the German first-line positions along the entire front and in some places penetrating and holding second-line positions. The scene of General Nivelle's great victory was the historic line of the Aisne, to which the Germans had retreated after the battle of the Marne. Ever since that epoch-making event in the history of the Great War the Germans had held the line despite every effort of the Allies to dislodge them. The Germans had ample warning that a great offensive was in preparation, for the French had been bombarding their positions for ten days before. On their part they had made every effort to repel the threatened attack, and had massed a great number of men and guns in that region. In justice to the Germans it must be said that they fought with courage and desperation along the whole front. They realized the importance of holding the line at all costs, for if the French advance proved successful, it would mean the isolation of Laon, upon which the Hindenburg line depended. North of Berry-au-Bac, where the old line of battle swings to the southeast toward Rheims, the French forces gained their greatest advance. To the south of Juvincourt they succeeded in penetrating the German second-line positions and held on. Every effort made by the Germans during the day failed, the French artillery literally tearing their ranks to pieces. Further advances were made by the French to the banks of the Aisne Canal at the villages of Courcy and Loivre.