It is natural that, in early myths, no accurate distinction should have been drawn between the sea and rivers with which the Aryans were familiar. The Caspian was imagined a broad river bounding the habitable earth, the origin of the Oceanus of the Greeks; and the sea of death is, in its earliest form, a river of death. All after-forms of mythical geography, moreover, such as we find among Indians, Greeks, or Norsemen, are but graftings upon this central idea. As the Aryans changed their homes, the new experiences gradually blotted out the old. The Greek transferred his thoughts about the Caspian to the Mediterranean, and when his geography extended, the Oceanus was pushed farther and farther away, until the later Euhemerist geographers came to confound it with the Atlantic. Thus it is but by accident that we give to ocean the meaning which it now bears. The first ocean was the mythical river which flowed round the earth, and the real physical forerunner of the myth was not the Atlantic or any of our oceans, but the Caspian Sea as it stretched before the eyes of the ancient Aryan folk. The Norseman, especially the Icelander,[13] lived so close to the ocean, that the older myth was forgotten beside the aspect of nature so familiar to him. In the middle of his earth stood a high mountain, on which was a strong city, Asgaard, the house of the Æsir or gods. Below Asgaard lay the green and fruitful earth, man's home. Then outside flowed or lay the great mid-earth ocean, just like the Greek ocean in character, despite all differences of climate and country. At other times the mid-earth sea is personified as a devouring monster, Jörmungandr ("great monster"), the name of the mid-gaard serpent who lies at the bottom of the encircling sea, shaking the earth when he moves.[14] Beyond, lies the ice-bound land of giants--Jötunheim, giant's home--dark like the Cimmerian land, and peopled with beings as weird and terrible as the Cyclops or the Gorgons. Gradually the myths of the river of death and the sea of death from being one became two. The second was confined to those nations who lived upon the sea-shore, and lost in great part its early shape; but neither Indians, Greeks, nor Norsemen forgot the myth of the mortal river. The Indian retained it singly; for when his turn for wandering came, he passed over the eastern mountains and reached a land where no sea was any longer to be seen or heard of. In the mythical language of the Vedas, the mortal river is called Vaitera_n_i; it lies "across the dreadful path to the house of Yama,"[15] the god of Hell.