The trees and bushes which clothed its sides concealed the infantry which was doubtless lying there, but in the valley just below them they could see a battery of heavy guns thundering against the Belgian fort. So rapidly were they served that the roar of their discharge was almost continuous, while high above it rose the scream of the shells as they hurtled toward their mark. There was something fascinating in the precise, calculated movement of the gunners--one crouching on the trail, one seated on either side of the breech, four others passing up the shells from the caisson close at hand. Their officer was watching the effect of the fire through a field-glass, and speaking a word of direction now and then. Their fire was evidently taking effect, for it was this battery which the gunners in the fort were trying to silence--trying blindly, for the German guns were masked by a high hedge and a strip of orchard, and only a tenuous, quickly-vanishing wisp of white smoke marked the discharge. So the Belgian gunners dropped their shells hither and yon, hoping that chance might send one of them home. They did not find the battery, but they found other marks--a beautiful white villa, on the first slope of the hillside, was torn asunder like a house of cards and a moment later was in flames; a squad of cavalry, riding gayly back from a reconnoissance down the river, was violently scattered; a peasant family, father and mother and three children, hastening along the road to a place of safety, was instantly blotted out. It was evident now that the Meuse was the barrier which had stopped the army. Far up toward Liège were the ruins of a bridge, and no doubt all the others had been blown up by the Belgians. Down by the river-bank a large force of engineers were working like mad to throw a pontoon across the swift current. The material had already been brought up--heavy, flat-bottomed boats, carried on wagons drawn by motor-tractors, great beams and planks, boxes of bolts--everything, in a word, needed to build this bridge just here at a point which had no doubt been selected long in advance! The bridge shot out into the river with a speed which seemed to Stewart almost miraculous. Boat after boat was towed into place and anchored firmly; great beams were bolted into position, each of them fitting exactly; and then the heavy planks were laid with the precision and rapidity of a machine. Indeed, Stewart told himself, it was really a machine that he was watching--a machine of flesh and blood, wonderfully trained for just such feats as this. "Look! look!" cried the girl, and Stewart, following her pointing finger, saw an aëroplane sweeping toward them from the direction of the city. Evidently the defenders of the fort, weary of firing blindly at a battery they could not see, were sending a scout to uncover it.