By the end of the two following days--the 5th and 6th--the investment was almost complete, and the communication with the surrounding country interrupted. On the evening of the 9th there came another summons from the enemy's general, declaring that if the place were not surrendered within twenty-four hours the bombardment would commence. The colonel replied as before. In fact, on the 10th of February a mortar battery opened fire, first on the northern salient, about eight o'clock in the evening. The bombs produced no effect, and in ten hours' bombardment only eight men had been struck, the roof of one of the barracks broken in, and two gun-carriages damaged. The pieces of large calibre mounted on the cavaliers of the bastions of the work did not begin to fire on the mortar battery until daybreak, and silenced it about noon. The enemy appeared then to limit his efforts to the investment; and it was not till the 17th of February, probably in consequence of news received from the north, that he appeared to decide on a regular siege. Perhaps until this moment he had not the needful appliances. On the night of the 17th, the first parallel was commenced about six hundred yards from the salient of the re-entering _place d'armes_ (Fig. 70), as also the communications between this parallel and the depôts. About two o'clock in the morning the governor sent out a hundred and fifty men, who charged the advanced posts protecting the workmen on the western side of the plateau, and forced their passage through to the trench; put the sappers to rout, took some of their tools, and then, seeing themselves taken in flank, rushed up the slopes of the plateau, and re-entered by the postern of the lower town, protected by the fires of the demi-bastion. On the 18th of February those who worked by day finished what their comrades, told off for night work, had commenced; and the engineers fixed in the parallel the prolongations of the works of the place, which they were intending to ricochet, with a view to planting the first batteries. By the method in which the besieger was proceeding, Colonel Dubois and Captain Allaud had no difficulty in perceiving that they had to do with a methodical enemy, who would conduct his attack according to the rules of the art, and would employ the acknowledged methods of approach against the main work of La Roche-Pont. The commander of the Bavarian engineers, in fact, had drawn out the plan of siege as exhibited in Fig. 70. On the night of the 18th of February he commenced the ricochet batteries of the first parallel, and the boyaux of communication that were to lead to the second parallel; the works were continued by day. He was intending to direct the siege in the method we are going to describe. On the third night the batteries of the first parallel were completed so as to fire in concert at daybreak.