After the Battle of Marathon ten years earlier, in 490 BCE, the Athenian statesman Themistocles outlined a military defensive program against the Persian invaders that was based entirely on sea power. As Plato put it, "Themistocles robbed his fellow-citizens of spear and shield, and degraded the people of Athens to the rowing-pad and the oar." Construction work in Piraeus had already begun in 493 BCE (also on Themistocles advice). Now, recent underwater excavations conducted by ZHP Project, which combines land and underwater archaeology of the ancient Zea and Mounichia harbors in Piraeus, have uncovered naval bases and huge fortifications that...