Of the three principal conditions, the first, situation, is the most indispensable; because strength and resources can be artificially supplied or increased, but it passes the power of man to change the situation of a port which lies outside the limits of strategic effect. Generally, value of situation depends upon nearness to a sea route; to those lines of trade which, when drawn upon the ocean common, are as imaginary as the parallels of the chart, yet as really and usefully exist. If the position be on two routes at the same time, that is, near the crossing, the value is enhanced. A cross-roads is essentially a central position, facilitating action in as many directions as there are roads. Those familiar with works on the art of land war will recognize the analogies. The value becomes yet more marked if, by the lay of the land, the road to be followed becomes very narrow; as at the Straits of Gibraltar, the English Channel, and in a less degree the Florida Strait. Perhaps narrowing should be applied to every inlet of the sea, by which trade enters into and is distributed over a great extent of country; such as the mouth of the Mississippi, of the Dutch and German rivers, New York harbor, etc. As regards the sea, however, harbors or the mouths of rivers are usually _termini_ or _entrepôts_, at which goods are transshipped before going farther. If the road be narrowed to a mere canal, or to the mouth of a river, the point to which vessels must come is reduced almost to the geometrical definition of a point and near-by positions have great command. Suez presents this condition now, and Panama soon will. Analogously, positions in narrow seas are more important than those in the great ocean, because it is less possible to avoid them by a circuit. If these seas are not merely the ends—“_termini_”—of travel but “highways,” parts of a continuous route; that is, if commerce not only comes to them but passes through to other fields beyond, the number of passing ships is increased and thereby the strategic value of the controlling points.... [Illustrations are here employed to show that, owing to the freedom of movements on the open sea, dangerous positions when not located in narrow channels are more easily avoided than on land. Hence “_fausses routes et moments perdus_,” in Napoleon’s phrase, play an important part in naval operations, as shown by Napoleon’s route to Egypt via Malta and Crete, and Rozhestvensky’s choice of routes before Tsushima. On the other hand, obstacles when they exist are impassable. Only submarines can avoid danger by transit over land.—EDITOR.] II. _Military Strength_