A further, and in its way a more convincing argument in support of the mountain-origin theory is afforded by the early art of the Sumerians. On the most primitive seal cylinders[1] we find trees and animals whose home is in the mountains, and which certainly were not native to the low-lying plain of Babylonia. The cypress and the cedar-tree are only found in mountainous districts, but a tree which must be identified with one or the other of them is represented on the early seal cylinders; it is of course true that ancient Sumerian rulers fetched cedar wood from the mountains for their building operations, and therefore the presence of such a tree on cylinder seals merely argues a certain acquaintance with the tree, but _ceteris paribus_ it is more reasonable to suppose that the material earthly objects depicted, were those with which the people were entirely familiar and not those with which they were merely casually acquainted. Again, on the early cylinders the mountain bull, known as the _Bison bonasus_, assumes the rôle played in later times by the lowland water-buffalo. This occurs with such persistent regularity that the inference that the home of the Sumerians in those days was in the mountains is almost inevitable. Again, as Ward points out, the composite man-bull Ea-bani, the companion of Gilgamesh, has always the body of a bison, never that of a buffalo. So too the frequent occurrence of the ibex, the oryx, and the deer with branching horns, all argues in the same direction, for the natural home of all these animals lay in the mountains. The Mesopotamian valley may, for the immediate purpose of this book, be divided into two halves, a dividing-line being roughly drawn between the two rivers just above Abû Habba (Sippar); the northern half embraces the land occupied by the Assyrians, and the southern half that occupied by the Babylonians. The precise date at which Assyria was colonized by Babylonia is not known, but to the first known native[2] king of Assyria, Irishum, we may assign an approximate date of 2000 B.C. Babylonia proper is an alluvial plain the limits of which on the east and west are the mountains of Persia and the table-land of Arabia respectively. This valley has been gradually formed at the expense of the sea’s domain, for in the remote past the Persian Gulf swept over the whole plain at least as far northward as the city of Babylon where sea-shells have been found, and probably a good deal further. It owes its formation to the silt brought down by the two rivers and deposited at the mouth of the Gulf: the amount of land thus yearly reclaimed from the sea in early times is not known, but as Spasinus Chorax the modern Mohammerah, which is now some forty-seven miles inland, was situated on the sea-coast in the time of Alexander, we know that the conquest of the land over the sea has been progressing since his time at the rate of 115 feet yearly.