This sea will also invite commerce if the Greeks have anything to sell. It does not look as if they will have much. A few valleys and small plains are fertile enough to feed their own proprietors, but as regards corn and food-stuffs Greece will have to be an importer, not an exporter. In history we find great issues hanging on the sea-routes by which corn came in from the Black Sea. Wine and olive oil are the only things that Nature allowed Greece to export. As for minerals, Athens is rich in her silver-mines, and gold is to be found in Thrace under Mount Pangæus. But if Greece is to grow rich it will have to be through the skill of her incomparable craftsmen and the shield and spear of her hoplites.[1] The map will help to explain another feature of her history. Although at first sight the peninsula looks as if it possessed a geographical unity, yet a second glance shows that Nature has split it up into numberless small plains and valleys divided from one another by sea and mountain. Such a country, as we see in Wales, Switzerland, and Scotland, encourages a polity of clans and cantons, each jealous of its neighbour over the hill, and each cherishing a fierce local patriotism. Nature, moreover, has provided each plain with its natural citadel. Greece and Italy are both rich in these self-made fortresses. The traveller in Italy is familiar with the low hills or spurs of mountains, each crowned with the white walls of some ancient city. If ever geography made [Illustration: FIG. 1. THE ACROPOLIS OF ATHENS] [Illustration: FIG. 2. THE CITADEL OF CORINTH Plate I _English Photo Co., Athens_] history, it was where those flat-topped hills with precipitous sides, such as the Acropolis of Athens and Acrocorinthus,[2] invited man to build his fortress and his shrine upon their summit. Then, perched safely on the hill-top and ringed with her wall, the city was able to develop her peculiar civilisation even in troubled times while the rest of the world was still immersed in warfare and barbarism. The farmer spends the summer in the plain below for sowing and reaping, the mariner puts out from harbour, the soldier marches out for a summer campaign, but the city is their home, their refuge, and the centre of their patriotism. We must not overrate the importance of this natural cause. Even the plains of Greece, such as Thessaly and Bœotia, never developed a unity. There too the citadel and the city-state prevailed. Geography is seldom more than a contributory cause, shaping and assisting historical tendencies, but in this case it is impossible to resist the belief that in Italy and Greece the hill-top invited the wall and the wall enabled the civilisation of the city-state to rise and flourish long in advance of the rest of Europe.