Just because the roads do not cling to the valleys, but strike across them at right angles, they are always crossing watersheds by means of difficult passes. And so there is hardly a route in the whole Peninsula where it is possible to find fifty miles without a good defensive position drawn across the path. Moreover, the continual passes make the question of supplies very difficult: in crossing a plain an army can live, more or less, on the supplies of the country-side; but among mountains and defiles there is no population, and therefore no food to be had. Hence an army on the move must take with it all that it consumes, by means of a heavy wagon train, or an enormous convoy of pack-mules. But only the best roads are suitable for wheeled traffic, and so the lines practicable for a large host are very restricted in number. The student is often tempted to consider the movements of the rival generals very slow. The explanation is simply that to transfer an army from one river-basin to another was a serious matter. It was necessary to spend weeks in collecting at the base food and transport sufficient to support the whole force till it reached its goal. In 1811 or 1812 the French and English were continually moving up and down the Portuguese frontier parallel to each other, the one from Salamanca to Badajoz, the other from Almeida or Guarda to Elvas. But to prepare for one of these flittings was such a serious matter that by the time that the army was able to move, the enemy had usually got wind of the plan, and was able to follow the movement on his own side of the frontier. There were months of preparation required before a few weeks of active operations, and when the concentration was over and the forces massed, they could only keep together as long as the food held out, and then had to disperse again in order to live. This was what was meant by the old epigram, that ‘in Spain large armies starve, and small armies get beaten.’