History of the Peloponnesian War

Themistocles also persuaded them to finish the walls of Piraeus, which had been begun before, in his year of office as archon; being influenced alike by the fineness of a locality that has three natural harbors, and by the great start which the Athenians would gain in the acquisition of power by becoming a naval people.

For he first ventured to tell them to stick to the sea and forthwith began to lay the foundations of the empire.

It was by his advice, too, that they built the walls of that thickness which can still be discerned round Piraeus, the stones being brought up by two wagons meeting each other. Between the walls thus formed there was neither rubble nor mortar, but great stones hewn square and fitted together, cramped to each other on the outside with iron and lead. About half the height that he intended was finished.

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.