After their definitive victory over the Persians in the Battle of Plataea, the Athenians fortified the city of Athens and the central harbour, Piraeus, with strong walls. Though mostly derelict now, sections are well preserved, notably near the Zea Marina (Pasalimani).

As early as 493 BC, Themistocles began to fortify the port, construction being completed under the rule of Cimon, in the mid-5th century BC. Defensive walls were extended, linking Piraeus to Athens. Torn down after the Athenian defeat in the Peloponnesian War, the walls were rebuilt by Conon in 394 BC when Athenian democracy was restored.