At length, on the 20th of February, the batteries of the first parallel, to the number of ten, opened their fire. Each of them was armed with three guns; the first on the right (of the besieger), à ricochet, raked the covered way in front of the right face of the left bastion (of the besieged). The second swept the right face of the left demi-lune; the third, the left face of the middle demi-lune; the fourth, à ricochet, raked the covered way in front of the left face of the left bastion; the fifth swept the salient of the demi-lune; the sixth swept the right face of that demi-lune; the seventh, à ricochet, raked the covered way in front of the left face of the right bastion; the eighth, à ricochet, raked the left face of the demi-lune in the centre; the ninth swept the left face of the right demi-lune; and the tenth, à ricochet, raked the covered way before the left face of the right bastion. Four mortars were mounted between the batteries 4 and 5, 6 and 7. Captain Allaud did not doubt that the principal attack would be directed to the left bastion; he had the gorge of this bastion therefore retrenched during the night. The six twenty-four pounders were placed in battery on the cavaliers of the bastions of the main defence, and well sheltered by traverses and blindages. These six pieces concentrated their fire on the fourth and fifth batteries of the besieger, and succeeded in silencing their fire about noon. Then they fired on battery No. 3, and before night silenced its three guns also. The guns in battery on the cavaliers of the bastions of the work were sufficiently well sheltered not to be in danger from the enemy's projectiles, to which they responded only feebly. But on the night of the 20th February the plans of the besieger had to be modified. At midnight the colonel ordered five hundred men to arm, put horses to his four field-pieces, whose wheels had been covered with rags and wool, and going out by the left demi-lune, he had two pieces placed on the right and two on the left of the road, two hundred yards in front of the glacis, and, on the road itself, the two howitzers, a hundred yards behind. Then he advanced resolutely towards the communicating boyau, between the third and fourth of the enemy's batteries, whose fire had been silenced. The posts offered but a slight resistance; the sappers fled, abandoning the trench, and were pursued to the batteries at the point of the bayonet. [Illustration: FIG. 70. THE THEORETICAL ATTACK ON VAUBAN'S WORK.]