The progress of the Turks was rapid with sap and mine. They were famed for their skill with entrenching and engineering tools, and the Christians learnt much from them, though their approaches were unlike the ordinary European works. Instead of parallel lines to the defences they drew curves, overlapping each other and continually approaching the place attacked. The trenches were deep, and fifteen or sixteen feet wide at the bottom where the ground allowed. The depth of the Turkish works effectually protected their soldiers, even when they had made a lodgment in the ditch; for the besieged could not depress their cannon sufficiently to hurt them.[9] They were protected skilfully by bomb-proof shelters of timber and of turf, beneath which thousands of men, hidden and shielded, crouched ready for attack, or for the repulse of sorties. Their mines penetrated in every direction to the counterscarp of the place, and ultimately to the walls themselves. At length the very cellars of the nearest houses were threatened by a subterranean enemy; and water and drums strewn with peas were placed in them, to tell, by the slightest vibration, of the work of the Turkish miner's pick below. The Turkish miners were bolder than those of the garrison. The latter were hired labourers of the lowest class, of whom Starhemberg wrote to Lorraine that nothing would induce them to re-enter a mine after they had heard the sound of the enemy working near them. On the part of the enemy, men who had applied for a _Timar_, or military fief, often volunteered as miners to prove their courage and to win its reward. At the very beginning of operations the city all but perished through a fire, which actually reached the windows of the Imperial arsenal stored with eighteen hundred barrels of powder. An explosion there would have opened a road for the Turkish army into Vienna, at once deprived of the means of resistance and reduced to ruins. The exertions of Captain Count Guido Starhemberg, nephew of the commandant, who personally superintended the removal of the powder through the opposite windows, together with a lucky change of wind, saved the city. Rightly or wrongly, an incendiary was suspected. The fear of treachery was added to the legitimate terrors of the citizens. Desertions took place to the enemy, and spies were actually apprehended within the walls. Hungarians and other Christians were arrayed upon both sides, and this community of language and manners, between besiegers and besieged, rendered such a danger more real. But from the open force of the attack the worst calamities were to be feared. On the 23rd, 25th, and 27th of July the opening assaults were delivered. All were repulsed, but with loss of lives ill-spared.