Since it is from the land, as the inhabited portion of the earth's surface, that all maritime movements emanate, and to the land that all oversea migrations are directed, the reciprocal relations between land and sea are largely determined by the degree of accessibility existing between the two. This depends primarily upon the articulation of a land-mass, whether it presents an unbroken contour like Africa and India, or whether, like Europe and Norway, it drops a fringe of peninsulas and a shower of islands into the bordering ocean. Mere distance from the sea bars a country from its vivifying contact; every protrusion of an ocean artery into the heart of a continent makes that heart feel the pulse of life on far-off, unseen shores. The Baltic inlet which makes a seaport of St. Petersburg 800 miles (1,300 kilometers) back from the western rim of Europe, brings Atlantic civilization to this half-Asiatic side of the continent. The solid front presented by the Iberian Peninsula and Africa to the Atlantic has a narrow crack at Gibraltar, whence the Mediterranean penetrates inland 2,300 miles (3,700 kilometers), and converts the western foot of the Caucasus and the roots of the Lebanon Mountains into a seaboard. By means of the Arabian Sea, the Indian Ocean runs northward 1,300 miles (2,200 kilometers) from Cape Comorin to meet the Indus delta; and then turns westward 700 miles farther through the Oman and Persian gulfs to receive the boats from the Tigris and Euphrates. Such marine inlets create islands and peninsulas; which are characterized by proximity to the sea on all or many sides; and in the interior of the continents they produce every degree of nearness, shading off into inaccessible remoteness from the watery highway of the deep. The success with which such indentations open up the interior of the continents depends upon the length of the inlets and the size of the land-mass in question. Africa's huge area and unbroken contour combine to hold the sea at arm's length, Europe's deep-running inlets open that small continent so effectively that Kazan, Russia's most eastern city of considerable size, is only 750 miles (1,200 kilometers) distant from the nearest White Sea, Baltic, and Azof ports. Asia, the largest of all the continents, despite a succession of big indentations that invade its periphery from Sinai peninsula to East Cape, has a vast inland area hopelessly far from the surrounding oceans. [Sidenote: Ratio of shoreline to area.]