62 THE POPULAR SCIENCE MONTHLY
Furthermore, the scarcity of gold and silver was beginning to be felt acutely about that time in Europe. After paying its eastern purchases with the precious metals for centuries the west had reached the stage in which its supply of coins was failing.
These are some of the economic conditions which led to westerly explorations in the course of which America was discovered.
The consolidation of Ottoman dominion in Europe after the fall of Constantinople marked the highest development of the strategic value of the waterways. This feature was considerably enhanced by the in- troduction of artillery as an arm about that time. Prior to the estab- lishment of the Turkish capital at Constantinople the strategic position of the straits had proved valuable in two important directions. For long it had acted as a natural moat defending European sections of the Byzantine Empire from Turkish attacks. In still earlier times and with the stronghold of Constantinople at its northern end the Eurasian ford had acted as the barrier deflecting barbarian invasions through Illyricum to Italy and the west. With armies and navies resting on the triple circle of Byzantine ramparts the narrow waterway was con- verted into a natural obstacle in the path of barbarian hordes which had succeeded in crossing the Danube in the course of recession from the northeast. Asia Minor, Syria and Egypt were thus spared the effects of the passage of invaders coming from the north.
The existence of the straits has profoundly affected the destinies of the Ottoman Empire. Turkey's disintegration marked by successive southeasterly recession of its European boundary was retarded consid- erably by the impregnable character of the defensive works constructed on the winding shores of the Dardanelles. This narrow strait attains a length of forty miles between the JEgean and the Marmora. A con- tracted channel, marked sinuosity of course and a line of hills on each shore commanding the intervening watery space provided all the ele- ments which nature could bring together to form a fortress.
In modern times the waterway has played an important part in the rivalry between western and eastern nations for its possession. In par- ticular, whenever the pressure of Slavic might tended towards a final effort to subjugate the Turk a convenient check could be promptly ad- ministered • by an armed force sent through the straits to protect the Sultan's capital.
The international status of the waterway has been affected by its intercontinental location. As a section of an important world route its fate concerned every nation whose subjects made use of this high- way. The long-deferred expulsion of Mongolians and Tatars from European soil can only be explained by the fact that the Turks de- scended from these races were the convenient masters of this important waterway. The occupation of this region by a power of the first mag-