Having made acquaintance with his corps, and finding that the French had not yet commenced their morning movements, Jack proceeded to complete his survey of the position. Beyond the River Huerba he could now clearly see the long rows of French trenches, the parallels cut here and there by a series of zigzags constructed with incredible labour to secure the besiegers’ approach to the walls. The French had actually made good their position on the near side of the river, immediately beneath the wall, towards Santa Engracia, but they had hitherto forborne to press their advantage, the height of the bank rendering it difficult for them to storm the ramparts in that quarter, and at the same time preventing them from blowing them up by mines. It was clear that no French attack was to be expected from the Porta Quemada side of his district, for in order to reach him the enemy would have to push their way through some hundreds of yards of streets held by Don Casimir, who had proved himself a very capable leader. But on the Santa Engracia side he was exposed to what was plainly the enemy’s principal attack. Their aim was obviously to reach the Coso, and to connect the wedge they were driving into the city in this quarter with the wedge already inserted at San Agustin. They had made considerable progress since the capture of the Santa Engracia convent four days before. They treated each block of houses as a miniature fortress. There was no attempt to carry it by storm until the defences had been attacked by sap and mine. As soon as a house was blown up they rushed in and occupied the ruins, where they entrenched themselves with bales of wool, gabions, and sacks of earth, and began to drive mines under the next block. Anxious to see for himself something of their method, Jack entered a house next to one recently blown up, and, ascending to the top story, peeped through a loop-hole pierced in the party wall. The roof of the next house had fallen in. Some charred beams were still smouldering. Here and there a tongue of flame licked the débris, and as the breeze blew in fitful gusts, dense clouds of smoke rose into the air. "They don’t do their work very thoroughly," said Jack to Don Cristobal. "The shell of the house is still standing. A good explosion would have shattered the whole place." "They have changed their ways, Señor," replied the lieutenant. "At first they used big charges and completely destroyed the houses; but they found that when the ruins cooled, and they occupied the space, they had no shelter from our fire. Now they use smaller charges and throw down only the wall next to them, leaving the other walls and the roof uninjured. The roof next door was not brought down by the explosion, but by our own men setting fire to the shell."