its existence.

For the fact that this priceless heritage was left to later ages
the world is indebted chiefly to the Greeks who fought at Salamis.
The night before that battle the cause of Greece seemed doomed
beyond hope. The day after, the invaders began a retreat that ended
forever their hopes of conquest. This amazing change of fortune was
due to the fact that the success of the Persian invasion depended
on the control of the sea. Hence the Greeks, though unable to muster
an army large enough to meet the Persian host on land, defeated
it disastrously by winning a victory on the sea.

2. THE PELOPONNESIAN WAR

After Salamis, Athens rose to a commanding position among the Greek
states. Her period of supremacy was brief, lasting less than 75
years, but while it endured it rested on her triremes. In the middle
of the fifth century she had 100,000 men in her navy, practically
as many as Great Britain in her fleet before 1914. Although the
period of Athenian supremacy was short-lived, it is interesting
because it produced a great naval genius, Phormio, and because
it wrecked itself as Persian sea power had done, in an attempt at
foreign conquest.

Scarcely had the Persian invasion come to an end when bickering broke
out among the various Greek states, much of it directed against Athens.
She had small difficulty, however, in maintaining her ascendancy in
northern Greece on account of her superiority on the sea, and it
was during the half century after Salamis that Athens arose to
her splendid climax as the intellectual and artistic center of
the world.

[Illustration: After Shepherd's _Historical Atlas._

THE ATHENIAN EMPIRE AT ITS HEIGHT--ABOUT 450 B.C.]

In 431 began the Peloponnesian War. Its immediate cause was the
help given by Athens to Corcyra (Corfu) in a war against Corinth.
Corinth called on Sparta for help, and in consequence northern and
southern Greece were locked in a mortal struggle. The Athenians
had a naval base at Naupaktis on the Gulf of Corinth, and in 429,
two years after war broke out, the Athenian Phormio found himself
supplied with only twenty triremes with which to maintain control
of that important waterway. At the same time Sparta was setting in
motion a large land and water expedition with the object of sweeping
Athenian influence from all of western Greece and of obtaining
control of the Gulf of Corinth. A fleet from Corinth was to join
another at Leukas, one of the Ionian Islands,