On 8 August, the Allied ground forces commander, General Bernard Montgomery, ordered the Allied armies to converge on the Falaise, Chambois area to envelop Army Group B, with the First US Army forming the southern arm, the British the base, and the Canadians the northern arm of the encirclement. The Germans began to withdraw on 17 August, and on 19 August the Allies linked up in Chambois. Gaps were forced in the Allied lines by German counter-attacks, the biggest being a corridor forced past the 1st Polish Armoured Division on Hill 262, a commanding position at the mouth of the pocket. By the evening of 21 August, the pocket had been sealed, with trapped inside. Many Germans escaped, but losses in men and equipment were huge. A few days later, the Allied Liberation of Paris was completed, and on 30 August the remnants of Army Group B retreated across the Seine, which ended Operation Overlord.