trees, and the field," and "its cold penetrated to the heart of the earth;" there the herds were tormented by the fly in the heat, bears and wolves fell upon the folds, and it was necessary to find protection against serpents and ravenous beasts of prey.[223] In this land life was a conflict against the heat of summer and the south, against the chill of winter and the mountain heights, a struggle for the maintenance and protection of the herds; and as soon as these tribes had become settled in the more favoured regions and passed over to agriculture, there began on the edge of those oases the struggle against the desert and the steppe. Here water must be conveyed to the dry earth, there the tillage must be protected against the sand-storms of the desert. To these difficulties and contrasts in the nature of the land was added a contrast in the mode of life of the population. The majority of the tribes of the table-land of the interior, and a part of the inhabitants of the mountainous rim, could not, owing to the nature of the land, pass beyond a nomadic pastoral life, and even to this day the population of Iran is to a considerable extent nomadic;[224] while other tribes toiled laboriously in the sweat of their brows, these wandered with their herds in idleness, ever ready for battle; and thus there could be no lack of ambuscades and plunder, of attacks and raids on the cultivated districts. All these contrasts are most marked on the slopes of the north-eastern edge, in Margiana, Bactria, and Sogdiana, which lay open to the steppes of the Caspian Sea. Here were fruitful, blooming valleys with luxuriant vegetation on the banks of the mountain streams, yet, wherever the mountains receded, the endless desert at once began. If the stars shone clear through the night on mountains and table-lands, in the pure and vapourless atmosphere of Iran, sand-storms and mist lay on the northern desert. The winds blowing from the north brought icy cold in the winter; in the summer they drove the sand of the deserts over the fruitful fields, to which water has to be laboriously conveyed in the time of the greatest heat, while eternal winter reigned in the heights of Belurdagh and Hindu Kush. There was also the continual fear of the nomads who dwelt on the steppes to the north, who made attacks on the fruitful slopes and valleys. We have already shown that it was precisely on the slopes of the Hindu Kush that the necessity of protection against the nations of the steppes led to a combination of the forces of the tribes who were settled there, and gave the impulse to the formation of a larger polity.