The French had gradually so extended their entrenchments outwards from Villejuif and Bruyeres, that they threatened to outflank the IInd Bavarian Corps. To thwart such a flank attack the VIth Corps was obliged to keep a strong force constantly in readiness at L'Hay. It need not be said that the supporting troops on the south front could nowhere be safe from the fire of the heavy fortress guns, nor the foreposts from that of the Chassepots. The latter consequently often could not be relieved for several days, and the relief was usually effected at night. The less the success of the French arms in the open field, the more lavish were they in the expenditure of ammunition from their works. Mont Valerien hurled its giant shells to a distance of from four to five miles, but this incessant cannonade, to the din of which the ear was soon accustomed, did little damage. THE ARTILLERY ATTACK ON THE SOUTHERN FRONT.--Till Mont Avron was taken, the Germans had only been able to oppose field guns to French fortress artillery. But early in January their preparations were at last so far forward that seventeen batteries, long since completed, could be armed with heavy guns against the south front of Paris. A battery stood apart on the left flank in the park of St. Cloud to the north of Sevres; four were close together on the steep slope of the height west of the Chateau Meudon; five on the edge of the plateau of Moulin de la Tour, where the mill, serving to guide the aim of the enemy, had been blown up. Four more batteries occupied a lower position between Fontenay and Bagneux. Two, between Chevilly and La Rue, served as protection against a flank movement from Villejuif, with the field artillery of the IInd Bavarian and VIth Corps. Dressing-stations were prepared, and intermediate depots were supplied with reserve ammunition from the great magazines at Villacoublay. Under Generals von Kameke[78] and Prince Hohenlohe[79] Colonels von Rieff and von Ramm conducted the artillery attack, General Schulz commanded the engineer attack. The men served twenty-four hours in the batteries, and then had two days' rest. The officers had but one day's rest. The heavy guns were brought up on January 3rd, by day, into the batteries which lay covered, without any interference; into all the others during the night, after the enemy's outposts had been driven in. Thus on the morning of the 4th 98 guns were ready to open fire: of these 28 were directed on Issy, 28 on Vanves, and 18 on Montrouge, 10 against the emplacements between the first two forts. But a thick fog hid every object, and it was not till January 5th at 8.30 in the morning, that the signal shot was given for opening fire.