Piraeus has been inhabited since prehistoric times. The settlement of Mounichia (the present Kastella) was created then. Themistocles, a political genius, later thought of utilizing this large natural harbour. He correctly noted the advantageous position of the three bays, existing in the area and convinced the Athenians to transfer their port from Phaliron to Piraeus.
After the Battle of Marathon- he built in 487 - 486 BC large fortification works and turned Piraeus into a military harbor.
The shipyards that were created then, built the mighty Athenian fleet, which distinguished itself at the Battle of Salamis.
The fortification of the harbor were completed by Kimon and Pericles with the construction of the Long Wall, by which Athens and Piraeus were joined. Its construction was completed in 456 BC. During its peak period the harbor of Piraeus contained 372 "neosoikoi" (sheds near the sea where ships were kept out of the water), "skevothikes" (the yards for the rigging of warships) and shipyards for the building of ships.