When we come to consider even the first of succeeding modifications we see still more clearly the complexity of any road-formulæ and the corresponding advantage of plan over habit. The marsh, the river, and the hill are but the beginning of the affair. There is a modification due to the fact that the marsh may not be permanent, nor the depth of the river; that the Road may be of special use at moments when the river is shallow or flooded, when the marsh is dry or, exceptionally, impassable. There is the modification of surface. Clay, for instance, is fairly good going in dry weather, but the worst in wet. There is the modification due to vegetation: the balancing of the effort involved in going round a dense scrub against that of cutting through it and of maintaining the cutting when it is established. There is the modification introduced by the instruments and science available for construction and for cutting. In one stage of development it will pay to take a road by a bridge across a deep river where in earlier stages of development it would have been necessary to seek a ford. In one stage of development it would pay to make a cutting through a scar too steep to climb where, in a lower civilization, it would have paid to go round it. The whole formula increases in complexity the more we examine it. It is a formula for the discovery of a minimum of effort. But in the establishment of that minimum you have to consider not only a very great number of factors, but the respective value of each to the whole, and your success in establishing the Road depends upon the accuracy of your judgment both as to the presence and as to the comparative value of all those factors. CHAPTER II THE CROSSING OF MARSH AND WATER _Physical Factors Modifying the Formula of the Road: Marsh as the Chief Obstacle to Travel: The Political Results of Marshes: The Crossing of Water Courses: The Origin of the Bridge: The Effect of Bridges upon Roads: The Creation of a Nodal Point: The Function of the Nodal Point in History._ i So much for the first principle of all: that the Road, like all other human institutions, is best made with brains, and for that second immensely valuable, but too often forgotten, political principle: that if you begin by making your thing wrong it is likely to take root and to remain wrong. A catalogue of the more important physical factors modifying the formula of the Road (I will come to the political and economic in a moment) is as follows: _Marsh to be traversed; water courses to be traversed; differences of surface other than marsh and water courses; gradients to be dealt with; the obstacle of vegetation to be dealt with._ To these five one may add a factor common to all, and to the making of every road, even in its most primitive stages: (6) the proximity of material (meaning by “proximity” the congeries of all the factors which make for the cheapness of material, for the advantage of using it in a particular place).