We have thus given, in some detail, descriptions of all the noteworthy experiments in navigation previous to the birth of Christ. Two features, it will be at once remarked, characterized all these efforts:--1st, The only reliable propelling force continued to lie in the oars; and, 2d, no sailor ventured out of sight of land, unless, as when crossing the Mediterranean, he knew that other lands lay beyond the visible horizon. We close this division of the subject with the general observation, that the opening of the Christian era found the world almost entirely under Roman dominion,--one which preferred extending its sway by land to prosecuting discovery by sea. The Mediterranean was, thus far, the only seat of commerce and the exclusive scene of navigation. Though Hanno and Eudoxus had indeed passed the Pillars of Hercules, and had coasted along the African shore as far as the negro territories, and though Pytheas, proceeding to the north, had visited--still hugging the land--the Baltic and the British Channel, their expeditions must be considered as at once venturesome and futile, for the age was not able to repeat them, and totally failed to make them useful either to geography or commerce. As long as the centre of power, of luxury, of wealth, remains within the Mediterranean, as long as Tyre, Sidon, Rome, Carthage, successively control the destinies of the world, so long shall we find mankind lacking both the motive and the means to seek new worlds, by sea, beyond. Time, however, will furnish both the motive and the means: we shall find the one, as we proceed, in the Spice Islands of the East, the other in the Mariner's Compass. The next division of our subject will narrate how the contests between the Crescent and the Cross over the tomb of Christ brought Europe and Asia into contact and acquaintanceship; and how the commerce and intercourse which were the immediate consequences led to that general and absorbing interest in the sea and ships which eventually produced Columbus and Magellan. The influence of nutmeg and cinnamon upon the spread of the gospel and the development of science is a theme which we shall show to be not unworthy of earnest and philosophical inquiry. [Illustration: SUPPOSED FORM OF THE SHIPS OF NEARCHUS.] [Illustration: VENETIAN GALLEY OF THE TENTH CENTURY.] Section II. FROM THE COMMENCEMENT OF THE CHRISTIAN ERA TO THE APPLICATION OF THE MAGNETIC NEEDLE TO EUROPEAN NAVIGATION, A.D. 1300. CHAPTER VIII. NAVIGATION DURING THE ROMAN EMPIRE--THE RISE OF VENICE AND GENOA--THE CRUSADES--THEIR EFFECT UPON COMMERCE--WEDDING OF THE ADRIATIC--CREATION OF THE FRENCH NAVY--INTRODUCTION OF EASTERN ART INTO EUROPE--MAPS OF THE MIDDLE AGES--REMOTE EFFECT OF THE CRUSADES UPON GEOGRAPHICAL SCIENCE.