Genghis Khan continued after this for two or three years in the Mohammedan countries of the western part of Asia, and extended his conquests there in every direction. It is not necessary to follow his movements in detail. It would only be a repetition of the same tale of rapine, plunder, murder, and devastation. Sometimes a city would surrender at once, when the conqueror approached the gates, by sending out a deputation of the magistrates and other principal inhabitants with the keys of the city, and with magnificent presents, in hopes to appease him. And they usually so far succeeded in this as to put the Mongul soldiery in good-humor, so that they would content themselves with ransacking and plundering the place, leaving the inhabitants alive. At other times the town would attempt to resist. The Monguls would then build engines to batter down the walls, and to hurl great stones over among the besieged. In many instances there was great difficulty in obtaining a sufficient supply of stones, on account of the alluvial character of the ground on which the city stood. In such cases, after the stones found near were exhausted, the besiegers would cut down great trees from the avenues leading to the town, or from the forests near, and, sawing the trunk up into short lengths, would use the immense blocks thus formed as ammunition for the engines. These great logs of heavy wood, when thrown over the walls, were capable of doing almost as much execution as the stones, though, compared with a modern bomb-shell--a monstrous ball of iron, which, after flying four or five miles from the battery, leaving on its way a fiery train through the air, descends into a town and bursts into a thousand fragments, which fly like iron hail in every direction around--they were very harmless missiles. In sawing up the trunks of the trees into logs, and in bringing stones for the engines, the Monguls employed the prisoners whom they had taken in war and made slaves of. The amount of work of this kind which was to be done at some of the sieges was very great. It is said that at the siege of Nishabur--a town whose inhabitants greatly offended Genghis Khan by secretly sending arms, provisions, and money to Jalaloddin, after they had once surrendered to the Monguls and pretended to be friendly to them--the army of the Monguls employed twelve hundred of these engines, all of which were made at a town at some distance from the place besieged, and were then transported, in parts, by the slaves, and put together by them under the walls. While the slaves were employed in works of this kind, they were sometimes protected by wooden shields covered with raw hides, which were carried before them by other slaves, to keep off and extinguish the fiery darts and arrows which were shot at them from the wall.