But the habit the Roman military engineers had of driving their roads in these great straight limbs, which are still so clearly marked, served many other purposes besides this military one of which I speak. It has been condemned as a waste of effort, for it is clear that a winding road, avoiding steep gradients and turning difficulties of marsh or wood, requires less effort to construct, mile for mile, than an artificially straight one; and that even when you have allowed for the extra length of a winding road, the formula of least effort will never give you a long straight. But your straight road has _the great advantage of rapid planning_. The Roman engineers, especially in the north--that is, in Belgium, Gaul, and in Britain--were working under campaign conditions, or in countries but recently occupied. They were under an imperative necessity of providing good communications as quickly as possible, and _for that object_ the straight road was obviously the best. Once you had determined the two points which you had to join, you established a track between them and carried it over all but the worst obstacles, taking all but the worst gradients. If you met marsh, you built a causeway; whenever you came to a river crossing, you threw your bridge; when you came to a sharp, narrow ridge you made a cutting. All that meant labour, but as in any case you were intending to make a great built, constructed, raised structure along the whole trajectory the extra labour involved in a straight trace was not proportionally as heavy as it would be for one of our ephemeral modern roads. In other words, the Roman engineers set out upon a plan necessarily expensive. They set out to make a great public monument, as it were; and the extra expense of its straightness did not weigh in the bill. ii A modification of this tendency to straight lines is found proceeding from three causes. First, where and when an established track already existed and the Roman work was only required to harden and strengthen it. Even there the Roman engineers would straighten portions which were too winding to fit in their scheme. But, apparently, where the track was fully established they tolerated a good many curves, especially if their work came some time after the conquest, when the land was settled. The second modification of the plan is to be found in hilly countries. In the mountains or very hilly regions the Roman engineers of necessity gave up the straight line, and as these regions were also the districts where on the heights large garrisons were least necessary they were the better able to abandon their general military plan.