To begin with, the geographical unity of the Italian peninsula is more apparent than real. The curving formation of the Apennines really divides Italy into four parts--(1) the northern region, mainly consisting of the Po valley, a fertile plain which throughout the Republican period was scarcely considered as part of Italy at all, and was, in fact, inhabited by barbarian Gauls; (2) the long eastern strip of Adriatic coast, an exposed waterless and harbourless region, with a scanty population, which hardly comes into ancient history; (3) the southern region of Italy proper, hot, fertile, and rich in natural harbours, so that it very early attracted the notice of the Greek mariners, and was planted with luxurious and populous cities long before Rome came into prominence; and (4) the central plain facing westward, in which the river Tiber and the city of Rome occupy a central position. Etruria and Latium together fill the greater part of it. Its width is only about eighty miles, so that there is no room for any considerable rivers to develop, and, in fact, there are only four rivers of any importance in a coast-line of more than 300 miles. We may call the whole of this region a plain in distinction from the Apennine highlands; but it is, of course, plentifully scattered with hills high enough to provide an impregnable citadel, and to this day crowned with huddled villages. Rome herself on her Seven Hills began her career by securing dominion over the Latin plain which surrounded her on all sides but the north. The Roman Campagna,[3] which is now desolate and fever-stricken, was once all populous farmland. The river Tiber, though its silting mouth and tideless waters now render it useless for navigation, was in the flourishing days of Ancient Rome navigable for small vessels and Ostia was a good artificial harbour at its mouth. Thus it is history rather than geography which has made Rome into an unproductive capital. We may conclude that geography has placed Rome in a favourable position for securing the control of the Mediterranean and especially of the western part of it.