Themistocles also now returned to his naval policy, and more ambitious undertakings that would increase the dominant position of his native state. He further extended and fortified the port complex at Piraeus, and "fastened the city to the Piraeus, and the land to the sea". Themistocles probably aimed to make Athens the dominant naval power in the Aegean. Indeed, Athens would create the Delian League in 478 BC, uniting the naval power of the Aegean Islands and Ionia under Athenian leadership. Themistocles introduced tax breaks for merchants and artisans, to attract both people and trade to the city to make Athens a great mercantile centre. He also instructed the Athenians to build 20 triremes per year, to ensure that their dominance in naval matters continued. Plutarch reports that Themistocles also secretly proposed to destroy the beached ships of the other Allied navies to ensure complete naval dominance—but was overruled by Aristides and the council of Athens.