If you take such a very old road as that of the primitive British trackway whose two branches, from Stonehenge and Winchester, unite in what is called the “Pilgrim’s Way” and make for the Straits of Dover, you find this trackway crossing the Mole, the Wey, and the Medway, as also the Darenth, at places where the obvious consideration has been a dry approach upon either side, and not the local shallowness of the stream. (We must remember in this connection that the word “ford” is used at plenty of places where the stream is too deep for crossing on foot: it means simply “a going.” A false etymology here has misled many historians.) Of more importance to the first makers of the Road than the depth of a water course was its swiftness. We have in this country few examples of swift streams of any magnitude, and none of streams so swift as to be impassable or passable with great difficulty, but where such examples occur abroad it is easy to see what a boundary and obstacle a rapid current afforded. It works in all manner of ways to the disadvantage of travel, it makes both swimming and ferrying more difficult (or impossible), it makes bridging either more difficult or (in early times) impossible, it usually connotes great differences of level, sudden floods, etc., and it also usually connotes changes and variety of currents, as well as the destruction of the banks. At an early stage in the development of the Road came the use of the bridge, and with the bridge the original chief consideration--a dry approach from either side--was emphasized. It is true that fords were bridged as roads developed, but the bridging of a ford is not the normal origin of the bridge. The normal origin of the bridge, if we judge by any one of the original great roads of Europe, is the replacing of a ferry. Men took the obstacle of a river (on account of its length) as something hardly to be turned, save perhaps in its higher reaches. They made straight for it, seeking only firm ground from which to embark and disembark, and established a boat crossing. To _this_ rather than to the ford the bridge succeeded. They bridged it with increasing success as their material science increased in power, and you may see all over Europe the great bridges thrown, not where the river was shallowest nor where it was easiest to traverse for any other reason, but chiefly where the main road led. In other words, the bridge is a function of the Road rather than the Road of the bridge.