Of the original home of the Sumerians, from which they came to the fertile plains of Southern Babylonia, it is impossible to speak with confidence. The fact that they settled at the mouths of the great rivers has led to the suggestion that they arrived by sea, and this has been connected with the story in Berossus of Oannes and the other fish-men, who came up from the Erythraean Sea and brought religion and culture with them. But the legend need not bear this interpretation; it merely points to the Sea-country on the shores of the Gulf as the earliest centre of Sumerian culture in the land. Others have argued that they came from a mountain-home, and have cited in support of their view the institution of the ziggurat or temple-tower, built "like a mountain," and the employment of the same ideogram for "mountain" and for "land." But the massive temple-tower appears to date from the period of Gudea and the earlier kings of Ur, and, with the single exception of Nippur, was probably not a characteristic feature of the earlier temples; and it is now known that the ideogram for "land" and "mountain" was employed in the earlier periods for foreign lands, in contradistinction to that of the Sumerians themselves.[57] But, in spite of the unsoundness of these arguments, it is most probable that the Sumerians did descend on Babylonia from the mountains on the east. Their entrance into the country would thus have been the first of several immigrations from that quarter, due to climatic and physical changes in Central Asia.[58] Still more obscure is the problem of their racial affinity. The obliquely set eyes of the figures in the earlier reliefs, due mainly to an ignorance of perspective characteristic of all primitive art, first suggested the theory that the Sumerians were of Mongol type; and the further developments of this view, according to which a Chinese origin is to be sought both for Sumerian roots and for the cuneiform character, are too improbable to need detailed refutation. A more recent suggestion, that their language is of Indo-European origin and structure,[59] is scarcely less improbable, while resemblances which have been pointed out between isolated words in Sumerian and in Armenian, Turkish, and other languages of Western Asia, may well be fortuitous. With the Elamites upon their eastern border the Sumerians had close relations from the first, but the two races do not appear to be related either in language or by physical characteristics. The scientific study of the Sumerian tongue, inaugurated by Professors Zimmern and Jensen, and more especially by the work of M. Thureau-Dangin on the early texts, will doubtless lead in time to more accurate knowledge on this subject; but, until the phonetic elements of the language are firmly established, all theories based upon linguistic comparisons are necessarily insecure.