History of the Peloponnesian War

Themistocles also persuaded them to build the remaining walls of the Piraeus, (they had been begun by him before, at the time of his office as archon, which he had held for a year over the Athenians,) thinking that the site was a fine one, as it contained three natural harbours; and that by becoming a naval people they would make a great advance towards the acquisition of power.

For he was the first who ventured to tell them that they must apply closely to the sea;

and he began immediately to assist in paving the way for their empire. It was by his advice that they built the walls of that thickness which is still seen round the Piraeus; for two waggons meeting each other brought up the stones. And in the inside there was neither rubble nor mortar, but large and square-cut stones wrought together, cramped on the outside with iron and lead. But only about half of the height he intended was finished.