At the time when Paris was fortified it was not foreseen that improvements in the artillery arm would double or treble the range of fire. The exterior forts, especially on the south, were at so short a distance from the enceinte that the city could easily be reached by the fire of heavy batteries. The Germans have been blamed for not having had recourse at an earlier date to this expedient of bombardment; but this criticism indicates an inadequate appreciation of the difficulties which stood in the way of its earlier execution. It may safely be accepted that the attack of a large fortified place in the heart of an enemy's country is simply impossible so long as the invader is not master of the railways or waterways leading to it, by which may be brought up in full quantity the requisite material. The conveyance of this by the ordinary highways, even for a short distance, is in itself a herculean undertaking. Up to this time the German army had the control of only one railway in French territory, and this was fully occupied in the maintenance of supplies for the armies in the field: in bringing up reinforcements and equipment; in conveying rearward wounded, sick and prisoners. But even this much of railway service ended at Toul; and the attempt to turn that fortress by laying a temporary section of line found insurmountable difficulties in the nature of the ground. Further forward there interposed itself a scarcely inferior obstacle in the complete destruction of the Nanteuil tunnel, to repair which would probably require weeks. Even then, for the further transport from Nanteuil up to the Paris front of 300 heavy guns with 500 rounds for each gun, there were requisite 4500 four-wheeled waggons, such as were not in use in the country, and 10,000 horses. Thus a bombardment was, in the earlier period, not to be thought of, and in any case the object of it would not be to destroy Paris, but merely to exert a final pressure on the inhabitants; and this influence would be more effectual when a long blockade had shaken the resolution of the besieged than it was likely to be at the beginning of the investment. _September 18th._--Corresponding directions communicated to the respective army commands, ordered the resumption of the march on the enemy's capital. On the 18th the Army of the Meuse, swinging leftward, had the XIIth Corps at Claye, the Guard Corps at Mitry, and the IVth Corps at Dammartin, one march from Paris. All the villages in front of St. Denis were occupied by the French. It seemed as if the investment on the north front of Paris would be resisted, and the Crown Prince of Saxony took measures for next day to follow up and support the IVth Corps, which led the advance. The 5th and 6th Cavalry Divisions, hastening on to Pontoise, were given two companies of Jaegers and a pontoon train, and after a bridge had been laid they crossed the Oise.