There were now 96 rifled cannon pieces and 38 mortars in full fire at very short range. Each gun was authorized to fire twenty rounds a day and ten shrapnel each night. The large Finkmatt Barracks were destroyed by fire, and the Stone Gate was so much injured that it had to be buttressed with sandbags. The garrison withdrew the guns behind the parapet, and only fired their mortars. However, in order to push forward the siege-works, sap-rollers had to be brought into use.
When it was discovered that mining galleries were being driven in front of lunette No. 53, Captain Ledebour let himself down by a rope into the ditches, and with the help of his pioneers removed the charges of powder.
During the night of the 13th--14th, the crest of the glacis in front of both the lunettes Nos. 52 and 53 was reached. The crowning was then begun by means of the double traverse sap, and was finished in four days.
The attack henceforth was exclusively directed against bastion No. 11.
To run off the water from the ditches of the fortress it was necessary to destroy the sluices by the Jews' Gate. These were invisible from any part of the field of attack, and the desired result could only be very incompletely obtained by artillery fire at a distance of more than a mile. Detachments of the 34th Fusilier Regiment, therefore, on the 15th, marched on the sluices under a heavy rifle fire from the besieged, and destroyed the dam.
The island of Sporen was at this time taken possession of by the Baden corps.
When the mortar-batteries had for the most part been moved up into the second parallel, the gun-batteries were also advanced nearer, and the wall-piece detachments did such execution by their accurate practice that the defenders never more dared to show themselves by day.
The retaining wall of lunette No. 53 could only be reached by indirect fire; but 1000 shells made a breach, and on the 19th September two mines were fired, which blew up the counterscarp and brought it down to the level of the water of the ditch. The pioneers immediately set about laying a dam of fascines across the ditch. A party sent over in a boat found the work abandoned. The gorge was closed under heavy rifle fire from the ramparts of the main fortress, and the parapet reversed so as to face the place.