But the bridge as a nodal point has yet another occasional function which has marked all history. That function it exercises when it is the lowest bridge upon a great navigable river. Such a bridge--the bridge of Rome for instance, the bridge of London, the bridge of Gloucester, the bridge of Newcastle, etc.--has been the making of inland ports. It must be remembered that before the advent of the railway, or at any rate before the organization of rapid and easy road travel, it was to the interest of sea-borne trade to penetrate into the heart of the country as far as possible. You avoided the cost of trans-shipment, and you had a much cheaper means of conveyance than anything that went by land. But the first permanent bridge across a waterway blocked the further progress up-stream of sea-borne traffic. Therefore there was a tendency to keep this first bridge well up-stream. Further, whenever it was made, it tended to create a glut of traffic at this point of section. The cargoes from the sea came here and could go no further, and this last function of the bridge is perhaps of all its historical functions the most important. Even where a river is very rapid, as the Tiber, the first bridge has some effect. Where it is tidal it is, of course, as in the cases we have just quoted, of the greatest effect, and usually on the great tidal waterways the first bridge will be found not indeed at the limit of the tide, for there the water would be too shallow, but in the last reaches. There are cases (Rochester is one) where the road has proved more important than the stream, where a bridge was imposed very low down in the tideway, but it has there fulfilled the same function of creating a market and a town. There are cases (Antwerp, Bordeaux, and Philadelphia are examples) where a secure harbour and good wharfage made the inland market and town in the absence of such an obstacle as the first bridge; but in the greater number of navigable rivers, even in so narrow a stream as that of Seville, the bridge makes the port and the town, as one can see by adding to the examples already given Nantes, Montreuil, Glasgow, etc.