History of the Peloponnesian War

His idea was by their size and thickness to keep off the attacks of an enemy; he thought that they might be adequately defended by a small garrison of invalids, and the rest be freed for service in the fleet.

For the fleet claimed most of his attention. He saw, as I think, that the approach by sea was easier for the king's army than that by land: he also thought Piraeus more valuable than the upper city; indeed, he was always advising the Athenians, if a day should come when they were hard pressed by land, to go down into Piraeus, and defy the world with their fleet.

Thus, therefore, the Athenians completed their wall, and commenced their other buildings immediately after the retreat of the Mede.