How did Athens strengthen its navy before Xerxes I’s invasion?

Before the invasion of Xerxes I in 480 BCE, Athens significantly strengthened its navy through a combination of strategic leadership and a fortunate economic windfall.

The Athenian politician Themistocles was the primary advocate for expanding the fleet. He recognized that the victory at Marathon could not be repeated against a larger Persian force and argued that Athens must become a dominant sea power to survive.1

The critical turning point occurred in 483 BCE, when a large surplus of silver was discovered in the state-owned mines at Laurium. Themistocles successfully persuaded the Athenian assembly to forgo a distribution of these funds to citizens and instead invest the entire amount into a massive shipbuilding program. This initiative increased the Athenian fleet from 70 ships to 200 triremes by 480 BCE.213

Additionally, Themistocles had earlier laid the groundwork for this naval expansion during his archonship in 493 BCE by initiating the construction of defensible harbors at Piraeus, which replaced the unprotected beaches of Phaleron.14