The Athenian who proposed blocking Persia by land at Thermopylae and by sea at Artemisium was Themistocles. His strategy paired a narrow-land-pass defence with a naval blockade, allowing the smaller Greek alliance to exploit geography and limit the Persian advantage in numbers.
The plan was adopted during preparations for Xerxes I’s second invasion of Greece in 480 BC. Thermopylae guarded the route south through central Greece, while Artemisium, on the northern tip of Euboea, helped prevent the Persian fleet from supporting or outflanking the army. The two engagements therefore formed a coordinated defensive operation rather than unrelated battles.
The strategy did not produce an immediate victory. The Greeks were defeated at Thermopylae, and the allied fleet withdrew from Artemisium after learning that the pass had fallen. Nevertheless, the delay helped the Athenians evacuate their city, and Themistocles later persuaded the allies to fight the Persian fleet in the confined waters of Salamis. That naval victory became a decisive turning point in the invasion. Cimon, Miltiades, and Pericles were prominent Athenian figures, but they were not the proposer of this 480 BC plan.