independence flourished
anywhere there would always be the threat of revolt in the Greek
colonies of Persia. Darius perceived rightly that the prestige and
the future power of his empire depended on his conquering Greece.

In 492 he dispatched Mardonius with an army of invasion to subdue
Attica and Eretria, and at the same time sent forth a great fleet to
conquer the independent island communities of the AEgean. Mardonius
succeeded in overcoming the tribes of Thrace and Macedonia, but the
fleet, after taking the island of Thasus, was struck by a storm
that wrecked three hundred triremes with a loss of 20,000 lives. As
the broken remnants of the fleet returned to Asia, leaving Mardonius
with no sea communications, and harassed by increasing opposition,
he was compelled to retreat also. In 490 Darius sent out another
army under Mardonius, this time embarking it on a fleet of 600
triremes which succeeded in arriving safely at the coast of Attica
in the bay of Marathon. While the army was disembarking it was
attacked by Miltiades and utterly defeated. The second expedition,
therefore, came to nothing. But Marathon can hardly be called a
decisive battle because it merely postponed the invasion; it affected
in no way the communications of the Persians and it did not weaken
seriously their military resources.

The great savior of Greece at this crisis was the Athenian,
Themistocles. He foresaw the renewed efforts of the Persian king
to destroy Greece, and realized also that the most vital point in
the coming conflict would be the control of the sea. Accordingly
he urged upon the Athenians the necessity of building a powerful
fleet. In this policy he was aided by one of those futile wars
so characteristic of Greek history, a war between Athens and the
island of AEgina. In order to overcome the AEginetans, who had a
large fleet, the Athenians were compelled to build a larger one,
and by the time this purpose was accomplished rumors came that
the Persian king was getting ready another invasion of Greece.

_Campaign of Salamis_

The third attempt was undertaken ten years after the second, in
the year 480, under Xerxes, the successor to Darius. This time the
very immensity of the forces employed was to overcome all opposition
and all misfortunes. An army, variously estimated at from one to
five million men, crossed the Hellespont on a bridge of boats to
invade the peninsula from the north, while a fleet of 1200 triremes
was