After having made the conquest of the Babylonian empire, Cyrus found himself the sovereign of nearly all of Asia, so far as it was then known. Beyond his dominions there lay, on every side, according to the opinions which then prevailed, vast tracts of uninhabitable territory, desolate and impassable. These wildernesses were rendered unfit for man, sometimes by excessive heat, sometimes by excessive cold, sometimes from being parched by perpetual drought, which produced bare and desolate deserts, and sometimes by incessant rains, which drenched the country and filled it with morasses and fens. On the north was the great Caspian Sea, then almost wholly unexplored, and extending, as the ancients believed, to the Polar Ocean. On the west side of the Caspian Sea were the Caucasian Mountains, which were supposed, in those days, to be the highest on the globe. In the neighborhood of these mountains there was a country, inhabited by a wild and half-savage people, who were called Scythians. This was, in fact, a sort of generic term, which was applied, in those days, to almost all the aboriginal tribes beyond the confines of civilization. The Scythians, however, if such they can properly be called, who lived on the borders of the Caspian Sea, were not wholly uncivilized. They possessed many of those mechanical arts which are the first to be matured among warlike nations. They had no iron or steel, but they were accustomed to work other metals, particularly gold and brass. They tipped their spears and javelins with brass, and made brazen plates for defensive armor, both for themselves and for their horses. They made, also, many ornaments and decorations of gold. These they attached to their helmets, their belts, and their banners. They were very formidable in war, being, like all other northern nations, perfectly desperate and reckless in battle. They were excellent horsemen, and had an abundance of horses with which to exercise their skill; so that their armies consisted, like those of the Cossacks of modern times, of great bodies of cavalry. The various campaigns and conquests by which Cyrus obtained possession of his extended dominions occupied an interval of about thirty years. It was near the close of this interval, when he was, in fact, advancing toward a late period of life, that he formed the plan of penetrating into these northern regions, with a view of adding them also to his domains.