After the Trojan War, the establishment of Greek colonies upon foreign coasts, the commercial intercourse with these colonies, and the very prevalent practice of piracy, contributed largely to the improvement of ships and of navigation. For many years no innovation was made upon the custom of employing ships with one rank of rowers on each side. The Erythræan Greeks are supposed to have invented the biremes, with two ranks, and the Corinthians the triremes, with three. Themistocles, in the fifth century B.C., persuaded the Athenians to build two hundred triremes, for the purpose of attacking Ægina. Even at this period, vessels were not provided with complete decks, some having partial decks, and some none at all, the only protection for the men consisting in the bulwark. The invention of decked ships is ascribed to the Thasians. After Alexander the Great, the Rhodians became the greatest maritime power in Greece. The Colossus of Rhodes, a brazen statue of Apollo, one hundred feet high, seems to have been erected in assertion of their commercial supremacy, for the legend is that it stood across the mouth of the harbor, and that vessels passed between its legs. Navigation still remained what it had been before, the Greeks seldom venturing into the open sea, and considering it necessary to remain in sight of the coast by day and to observe the rising and setting of the stars by night, in order to replace the landmarks no longer visible in the darkness. In winter, navigation was suspended altogether. Rather than double a cape, they would drag their vessel across a neck of land from one sea to another, by machines contrived for the purpose. This was frequently done across the Isthmus of Corinth. The ordinary size of a war-galley or trireme may be inferred from the fact that its complement of men was two hundred and thirty; and its speed in smooth water and with a favorable wind may be stated as very nearly that of a modern steamboat.