Let us take these physical points in their order. * * * * * ii MARSH. It is not always appreciated that the chief obstacle to travel from the beginning of time has been and still remains marsh, which may be defined as soil too sodden for travel, as distinguished from the lands which are boggy in wet weather but passable. Marsh is less striking to the eye, especially to the modern eye, than a stretch of water, much less striking than the apparent obstacle of the sea, or of a bold hill range: it is nevertheless the chief problem presented to the making of a road, because of all natural obstacles _it is the only one wholly untraversable by unaided man_. Man unaided can climb hills, swim water, work his way through dense undergrowth. But marsh is _impassable_ to him: it is the great original obstacle to progress. If this has not been recognized in the past, and is still little recognized, it is not only because marsh is less striking to the eye than water or hills, but still more because, the original roads established by man in forming his cities, markets, and all the rest of it, being compelled to avoid marsh, we do not often come across the problem even to-day. Partly, also, because very extensive marsh is a rare phenomenon, especially in Western Europe. But if we look at the map and at history we shall see what that obstacle means. It was marsh which cut off Lancashire from the South of England, and left Lancashire the stronghold of old institutions, especially after the Reformation. It was the marsh of the Lower Thames estuary, now upon the right, now upon the left bank of the river, which forbade a crossing below London. It was marsh which protected the growth of Venice at the earliest and most dangerous moment of its existence. It was marsh which cut off the Western (Polish) civilization from the Eastern (Russian) civilization, and was the main geographical cause of that sharp division in culture which has affected the whole of later European history. We may say that the Russian Orthodox Church and the last Revolution would neither have been, save for the Pinsk Marshes. To take lesser examples, we can see to-day the way in which even our modern ways avoid marsh. The large district of Gargano in Southern Italy has remained largely isolated through marsh upon its flanks. You may see all over Europe, and even in this well-drained country, primitive roads deflected through marsh as they are not by any other obstacle, and this deflection stamps our road system to this day, in spite of our enormously increased opportunities of road construction. We shall see on a later page the way in which marsh deflected in the dark ages Roman roads at the river crossings in this island.