The main advance was therefore to take place through Belgium, the Army of the Moselle co-operating, while to the Army of the Rhine was assigned the offensive-defensive role of advancing to the barrier fortresses of Epinal and Belfort to check any French advance that might be directed against the communications of the Armies of the Moselle and the Meuse to the north. The railroad communications through the Belgian plain were splendidly adapted to this plan, backed as they were by the military railroads which Germany had constructed several years before, running through the industrial districts in the north of the German Empire up to the Belgian border. Germany's first move was the invasion of Luxemburg, violating the neutrality of a State which, under the treaty making her independent and guaranteeing neutrality, (to which treaty Germany was a party,) was not permitted to maintain an army. Two days later Germany asked passage for her troops through Belgium, for the purpose of attacking France. Belgium promptly refused, and on Aug. 4 Germany began the forcing of this passage by an attack on Liege. Thus, at the outset the German plan went awry. Although the contemplated line of advance was through Liege and Namur, it was not sufficient, with Belgium openly in arms to defend her country, to reduce only these two towns. The Belgian Army could, and later did, fall back to the north on Louvain, Brussels, and Antwerp, and so be directly on the German flank and in a position to strike at the line of communications. It was therefore necessary to subjugate all of Belgium either by destroying the Belgian Army or driving it before them in their advance. Thus, the German advance was not only doomed to delay, but at least 100,000 troops were needed to garrison a hostile country and to protect the life lines running to the rear. Three days after the attack on Liege opened the Germans penetrated between the outer forts, their infantry advancing in close formation and sustaining enormous losses. But Liege was worth the price paid. Some of the forts held out for days, but were finally reduced by the fire of the 42-centimeter guns--the first of the German surprises. The Belgian garrison, however, had done its work. The German advance was delayed for ten precious days, during which the first consignment of the British expeditionary force had reached the Continent and France and Russia had largely completed their mobilization.