Happily, in the deserts they had to cross, Nature had allotted to the traveller occasional spots, though few and far between, where he could obtain rest for himself and his beasts of burden under the shade of a cluster of palm trees, with the additional refreshment of invigorating springs of cool, fresh water. These places of repose naturally became entrepôts of commerce, where merchants from all parts exchanged their commodities; and, hence, some of them, as Palmyra and Petra, became wealthy and magnificent cities, and the sites of temples and sanctuaries, to which the pilgrim and the merchant alike resorted. From these and other great centres, the leading caravans took their departure on their distant and dangerous journeys by routes as untraceable to the eye as the track of a ship on the ocean. [Sidenote: Their management.] The entire management or safe conduct of the great Asiatic and Arabian caravans was confided to the nomad tribes,[203] who provided the means of transport and directed their movements. In their hands was necessarily placed the important duty of breeding and rearing the camels,[204] and, in the transport of the goods of the merchants across the desert, they acted much as ship-owners now do in the conveyance of goods across the ocean; such duties, then as now, forming a separate and distinct branch of commercial enterprise. These undertakings vast in themselves—for it would require about four thousand camels to transport the amount of produce and manufactures constituting the cargo of a single modern Indiaman—formed an important trust. Articles of great value, in proportion to their bulk, such as silks, perfumes, balsams, and rich manufactures of various sorts, besides gold and silver, were entrusted to the care of those who had charge of the caravan, and who had dangers even greater to encounter than the perils of the sea. Nor was their responsibility limited to merchandise. All classes, as well as merchants, availed themselves of these caravans, so that arrangements had to be made on a large scale, and often for months before the caravan started, for the means of conveyance and for the requisite supply of water and provisions. [Sidenote: The more important routes.]