after empire, each becoming overgrown in the process, till at last the series was concluded by the Romans swallowing up the whole. It was this gradual spread of dominion which, at each stage, increased men's knowledge of surrounding nations, and it therefore comes within our province to roughly sum up these stages, as part of the story of geographical discovery.
Regarded from the point of view of geography, this spread of man's knowledge might be compared to the growth of a huge oyster-shell, and, from that point of view, we have to take the north of the Persian Gulf as the apex of the shell, and begin with the Babylonian Empire. We first have the kingdom of Babylon—which, in the early stages, might be best termed Chaldæa—in the south of Mesopotamia (or the valley between the two rivers, Tigris and Euphrates), which, during the third and second millennia before our era, spread along the valley of the Tigris. But in the fourteenth century B.C., the Assyrians to the north of it, though previously dependent upon Babylon, conquered it, and, after various vicissitudes, established themselves throughout the whole of Mesopotamia and much of the surrounding lands. In 604 B.C. the capital of this great empire was moved once more to Babylon, so that in the last stage, as well as in the first, it may be called Babylonia. For purposes of distinction, however, it will be as well to call these three successive stages Chaldæa, Assyria, and Babylonia.
Meanwhile, immediately to the east, a somewhat similar process had been gone through, though here the development was from north to south, the Medes of the north developing a powerful empire in the north of Persia, which ultimately
