There is also the question of durability. A primitive road, taking a very steep gradient, will be more durable than one taking a lesser gradient round the slopes of a hill and subject to falls from above and to degradation down the slope below; it will need less upkeep, for it is always shorter--and this last consideration explains what would otherwise be inexplicable: the extraordinarily steep gradients which primitive roads and even the roads of a high civilization will take. One of the best examples of this in England is the behaviour of the Fosse Way in the neighbourhood of Radstock in Somerset. Here the original road was presumably a prehistoric track, but we know that it was carefully remodelled by the high Roman civilization. It must have been used for the great mass of travel during four hundred years from the first occupation of the West of England by the Romans about A.D. 50 to the breakdown about 450, and right on into the Dark Ages--that is, for not less than one thousand years. During the first half of this time (and especially during the first third) it had to carry the travel of a very full, well-developed, and complex society to one of the most important centres of its wealth, the town of Bath. Yet the road goes up the most astonishing gradients. [Illustration: Sketch III] Somehow or other, these gradients were normally used--but it is a puzzle to say how. The modern road has frankly abandoned the effort, and takes a long sweep round both sides of the valley at a gradient of about 1 in 12. Even so, it is quite steep enough for our modern methods of travel.