Another stage in road evolution is well illustrated in many mountain regions, _i. e._ in the less-frequented parts of the Alps. Here the mountains are crossed by narrow tracks, which die away at intervals and then reappear. They are chiefly used by the herdsmen and cattle, during the periodical migrations to the higher pastures, and this fact gives rise to certain peculiarities. Where the region traversed is very steep the path is usually well marked, and there may be even attempts to improve difficult parts so as to render it more practicable. When the ground becomes more level the path dies away, or divides up into a multitude of minor tracks. The reason is obvious. In the steep regions the cows must keep together, and their constant journeyings render the road well marked. It must also be easy enough to permit of the passage of the animals, whose agility has its limits. Where the ground is level grass usually grows, and here the cattle spread out in all directions to feed, and the path naturally dies away. It may be marked on the map as going on to cross a col and so reach another valley, but as the number of persons making the traverse is likely to be small, the track is badly marked, as many a tourist has found to his cost. From such tracks, which are little more than aids in crossing specially difficult areas, to the well-made roads which traverse the civilised countries of the world the gap is great, for, though the Romans made magnificent roads, after their time there was a rapid decay in the art, and the well-kept roads of the western countries of Europe are things but of yesterday. With the development of tracks and roads, as distinct from a mere animal trail through the bush, there comes the possibility of using pack-animals and wheeled vehicles for transport. The two do not necessarily occur together. Thus in China and Japan wheeled vehicles are drawn by human beings, though in China the wheelbarrows drawn by human porters have also sails to aid their propulsion. The use of animals, whether as pack-animals or for traction, means a relatively high degree of civilisation, and means also a food supply normally more than enough for the human members of the community. In many parts of tropical Africa, despite the tropical luxuriance of many of the food plants, and the absence of winter, there is practically no food reserve, and the normal condition is that the whole group is within measurable reach of starvation, should any one of a whole series of probable or possible accidents happen to the plantations. Under such conditions large domestic animals, requiring great quantities of food, cannot be kept.