Some centuries passed, during which the Greeks sailed round the southern headlands of the Peloponnese into the Ionian Sea, and colonised along the shores of that sea also. So the peninsula came to be a citadel in the midst of the Greek sea-world. Along the outer shores of the twin waters, Ægean and Ionian, the Greek colonists were but a fringe exposed to attack from behind. Only in the central peninsula were they relatively, although as the sequel shows not absolutely, safe.
To the eastern, outer shore of the Ægean the Persians came down from the interior against the Greek cities by the sea, and the Athenian fleet carried aid from the peninsular citadel to the threatened kinsfolk over the water, and issue was joined between sea-power and land-power. A Persian sea-raid was defeated at Marathon, and the Persians then resorted to the obvious strategy of baffled land-power; under King Xerxes they marched round, throwing a bridge of boats over the Dardanelles, and entered the peninsula from the north, with the idea of destroying the nest whence the wasps emerged which stung them and flew elusively away. The Persian effort failed, and it was reserved for the half-Greek, half-barbaric Macedonians, established in the root of the Greek Peninsula itself, to
