We have seen that the main cause of the breaking down of the Roman Road was marsh and the crossing of river valleys. Not only was this process true of natural marshes, especially at the sides of a river, it was true of a special case which is reproduced over and over again on the map of England, and for which I will take as a particular example a very fine case near Norton Park, in Northamptonshire. [Illustration: _Part II_, Sketch X] Here the Watling Street, the great Roman road from London to the north-west, crossed the valley of an insignificant stream; there was no marsh originally, and there is none to-day. There was only a small running of water, over which a culvert was thrown. The stream ran under the main Roman embankment through this culvert. Now, when the Dark Ages came and the roads fell into disrepair the first things to go, naturally, were the culverts. They got blocked up. Once they got blocked up the water dammed up on the higher side and began to undermine the embankment. By the time this had made the road, though still standing, impassable, travel had found a new way, usually _down the stream_ away from the mere thus formed. Further centuries and the recovery of civilization cleared the ground: the embankment either was washed away or swallowed up in the mere and its subsequent marsh, the stream resumed its original course, the dry ground reappeared, but the trace of the Roman road upon either side across the depression was lost for ever and there was substituted for it the modern road, making a curve out of the direct line and only recovering it again after the obstacle had been passed. iii The gradual decay of the Roman Road in the Dark Ages was not everywhere the same, and the consequence is that the remaining fragments of Roman roads are connected in different ways with the modern road system which gradually grew out of them. There are four types--overlapping, of course--of the fate attaching to the Roman roads of this country. They are, as I have said, the root of all our road system. All English roads subsequent to the period of the Roman occupation have grown out of the great network laid down for ever by the Roman engineers. But the fortune which the original road suffered, the way in which a modern system developed from it, were not uniform. There were four divergent developments, which ran thus: (1) The Roman Road is preserved as a basis of the modern road, and remains a main artery: of this the great example is the Watling Street, in the first few days’ marches north-west of London. (2) The Roman Road remains clearly the basis of the system of local roads which developed from it, and, though disappearing in sections, is, upon the whole, preserved; of these the great example is the Stane Street road from Chichester to London.