On the opposite side, General von Tresckow (commanding 1st Reserve Division) had available at the outset, a force of not more than twenty weak battalions of Landwehr, five squadrons and six field-batteries, in all barely 15,000 men. He had at first to confine himself to a mere investment. The troops, intrenched in the villages round a wide circumference, had to repel many sorties. Orders were received from the supreme Headquarter to set about the regular siege of the place. General von Mertens was charged with the direction of the engineer operations, and Lieut.-Col. Scheliha with that of the artillery attack. The difficulties of the undertaking were obvious. The rocky nature of the soil could not but increase the labour of throwing up earthworks, and the cold season was approaching. The attack could be carried on successfully only from the south against the main work--the formidable citadel. Only fifty heavy guns were available for the time, and the infantry strength was not sufficient to efficiently invest the place on all sides. In these circumstances, there devolved on General von Tresckow the task of attempting the reduction of Belfort by a mere bombardment. Towards this purpose the attack was chiefly directed from the west, in which quarter, after the enemy's garrison had been driven out of Valdoye, the infantry occupied Essert and Bavilliers, as well as the adjacent wooded heights. On December 2nd seven batteries were constructed on the plateau between these two villages by 3000 men, under cover of two battalions. The hard-frozen ground added to the difficulties of the work; yet, notwithstanding the moonlight night, the operations would appear to have escaped the attention of the besieged. When on the following morning the sun had dispersed the fog and made visible the objects, fire was opened. The fortress replied at first but feebly, but afterwards with increasing vigour from the entire line of works, even from Forts La Miotte and La Justice at a range of 4700 yards, and the losses in the trenches were considerable. Four more batteries in front of Bavilliers were armed, and on the fall of La Tuilerie the infantry pressed on to within 170 yards of the enemy's most advanced trenches. The artillery fire caused a conflagration in the town; but the ammunition was soon exhausted, whilst the lofty citadel maintained unchecked an effective fire, and repeated sorties on the part of the garrison had to be repelled. It was now clear, since no decisive result had followed the methods hitherto resorted to, that only by a regular attack could that be attained.