The Road

by Hilaire Belloc

iii

How were these great straight limbs plotted out? That is a question which has been fully debated but not yet settled. Where two ends of a trajectory were in sight one from the other the matter was simple enough; but what was the method used when the straight line exceeded the horizon: when it was carried on, for instance, for more than thirty miles, as is the case over and over again in the great north-eastern road from Paris to Cologne, and in the road from Amiens to Boulogne? What was the method when, even for lesser distances, one end of the trajectory could not be seen from the other on account of intervening hills, or where in flat land forests were sufficient to impede the view?

One theory has been that of smoke signals, a method which has been found of use, I believe, in barbarous countries in our own day. We must, I think, certainly reject it in such a climate as ours. Such signals could only here be used upon a few days in the year, specially picked, and the Roman engineers would not have depended upon the caprice of the weather. There has also been suggested (I adopted that suggestion myself in the monograph of which I have just spoken) the use of high movable platforms, but I now think that this also should be rejected on account of its clumsiness, and of the fact that in an uncleared country it would often be quite impractical. The most probable method was suggested to me by a correspondent some years ago, based upon his own experience in the planning of roads in new countries. It is the method of odds and evens, and requires some description with the aid of a simple plan.

Suppose that you have to construct a straight line from A to B, A and B not being visible one from the other, and the distance between them being considerable. If you have plenty of men with which to work (and the Roman military commanders did not lack these), you will proceed as follows: You send out your men from either end, in two chains as it were, each individual easily in sight of his next neighbour, but not nearer to him than is necessary for the observation of signals. These chains of men are either directed from the two ends of the line, or, if you can work only from one end, you send them out from that end, instructing the head of the chain when he comes in sight of the other end to work towards it and establish himself there. At the end of the process, whether you have been working with two lines approaching each other from either end and joining hands in the middle, or from one end only, you will end up with a line which will certainly not be straight—on the contrary, very irregular—but which will at least join your two goals. Probably, if you had been working from both ends, A and B, you would have something like [sketch VI]; while if you be working from one end only—A—the head of your column would probably be widely out at the conclusion of your experiment. Your column would have to double back sharply on to its goal when at last it was caught sight of, and you will have some such trace as on [sketch V].

Part II, Sketch V Part II, Sketch VI

At any rate, having established this rough winding line, you next make the men number themselves as a line does when it is dressing, by odds and evens, or by ones and twos, so that the first, third, fifth, seventh man, etc., counting from one end make one lot, or all the ones make one lot, if you are going by ones and twos—and the second, fourth, sixth, eighth man, and so on, make another lot. You bid one of these sets—say the odds—to face towards one goal—say B—and the other set to face towards the other goal—A. Lastly, you bid them space themselves out so that any individual of one set can at least clearly see his fellow in the same set along the direction to which he faces, and the man of the other set in between. For instance, No. 39, looking south towards B, must be able to see No. 37, who is facing the same way as he is, and must at the same time be able to see No. 38, who is facing towards him; similarly, No. 38 must be able to see No. 40 clearly, and No. 39 in between. It is clear that in thick, “blind” country (as, for instance, in woods or in tumbled land) your men will have to stand fairly close together. But in open country they can be at considerable distances—up to half a mile or more; so long as every unit can see the next unit of the same set clearly, and have his signals received by the unit of the other set in between, the conditions are satisfied. Your line being thus instructed (and, as anyone may discover in practice, it is not a very long business once the first rough chain has been established), the numbers of each set signal to the intervening numbers of the other set alternatively to move to right or left until a straight line is locally established.

Part II, Sketch VII Part II, Sketch VIII

For instance, in [sketch VII] you begin with the “evens,” looking northward. No. 38, looking north towards No. 40, sees that No. 39 (who faces him, looking south) is somewhat too much to the east and does not stand properly between him and No. 40. He signals to No. 39 to move westward as along the dots until No. 39 is at a new position, shown by the dotted circle exactly between No. 38 and No. 40. Next, No. 36 signals to No. 37, who is too much to the west, until No. 37 is exactly between himself and No. 38. When this has been done all along the line by the evens the order is given to the odds to repeat the process from their new positions. No. 39, looking southward from his new position at the dotted circle, sees that No. 38 is too far to the east to be in perfect alignment with No. 39’s next odd neighbour No. 37, at whom he is looking, southward. No. 39 signals, therefore, to No. 38, who is looking northward, to move westward, and No. 38 does so until the signal stops him, when he is just in line between the new positions of No. 39 and No. 37.

It will be evident that after this first stage of the process the original irregular line between A and B will have been much straightened. You have but to repeat the manœuvre half a dozen or a dozen times to get the whole body of men into a strictly straight line between the two extremities many miles apart, and that although those in the middle cannot see either extreme and neither extremity can see the other. In theory this method can be used for an indefinite extent of country. In practice it seems to have been used (if it were indeed that upon which the Roman engineers relied) for spaces sometimes as great as a three days’ march, and quite often as great as one day’s march or more.