_Assyria Proper_ lay east of the Tigris and west of the Median Mountains. The great empire which bore that name varied in extent under different monarchs, and the name of Assyria is often applied to all the territory between the Zagros Mountains and the Mediterranean Sea. The region between the two great rivers and north of Babylonia was called by the Greeks _Mesopota´mia_. It differed from the more southerly province in being richly wooded: the forests near the Euphrates more than once supplied materials for a fleet to Roman emperors in later times. _Susiana_ lay along the Tigris, south-east of Assyria. It was crossed by numerous rivers, and was very rich in grain. Its only important city was Susa, its capital. =23.= _Babylonia_ comprised the great alluvial plain between the lower waters of the Tigris and Euphrates, and sometimes included the country south of the latter river, on the borders of Arabia Deserta, which is better known as _Chaldæ´a_. When the snows melt upon the mountains of Armenia, both rivers, but especially the Euphrates, become suddenly swollen, and tend to overflow their banks. In fighting against this aggression of Nature, the Babylonians early developed that energy of mind which made their country the first abode of Eastern civilization. The net-work of canals which covered the country served the three purposes of internal traffic, defense, and irrigation. Immense lakes were dug or enlarged for the preservation of surplus waters; and the earth thrown out of these excavations formed dykes along the banks of the rivers. The fertile plain, so thoroughly watered, produced enormous quantities of grain, the farmer being rewarded with never less than two hundred fold the seed sown, and in favorable seasons, with three hundred fold. We shall not be surprised, therefore, to learn that Babylonia was, from the earliest times, the seat of populous cities, crowded with the products of human industry, and that its people long constituted the leading state of Western Asia. Though the plain of Babylonia afforded neither wood nor stone for building, Nature had provided for human habitations a supply of excellent clay for brick, and wells of bitumen which served for mortar. (Gen. xi: 3.)