ten new ones, named after legendary heroes of Greece and having no class basis, which acted as electorates. Each tribe was in turn divided into three trittyes (one from the coast; one from the city and one from the inland divisions), while each trittys had one or more demes, depending on their population, which became the basis of local government. The tribes each selected fifty members by lot for the Boule, the council that governed Athens on a day-to-day basis. The public opinion of voters could be influenced by the political satires written by the comic poets and performed in the city theaters. The Assembly or Ecclesia was open to all full citizens and was both a legislature and a supreme court, except in murder cases and religious matters, which became the only remaining functions of the Areopagus. Most offices were filled by lot, although the ten strategoi (generals) were elected. The silver mines of Laurion contributed significantly to the development of Athens in the 5th century BC, when the Athenians learned to prospect, treat, and refine the ore and used the proceeds to build a massive fleet, at the instigation of Themistocles. In 499 BC, Athens sent troops to aid the Ionian Greeks of Asia Minor, who were rebelling against the Persian Empire (see Ionian Revolt). That provoked two Persian invasions of Greece, both of which were repelled under the leadership of the soldier-statesmen Miltiades and Themistocles (see Persian Wars). In 490 the Athenians, led by Miltiades, prevented the first invasion of the Persians, guided by king Darius I, at the Battle of Marathon. In 480 the Persians returned under a new ruler, Xerxes I. The Hellenic League led by the Spartan King Leonidas led 7,000 men to hold the narrow passageway of Thermopylae against the 100,000–250,000 army of Xerxes, during which Leonidas and 300 other Spartan elites were killed. Simultaneously the Athenians led an indecisive naval battle off Artemisium. However, that delaying action was not enough to discourage the Persian advance, which soon marched through Boeotia, setting up Thebes as their base of operations, and entered southern Greece. That forced the Athenians to evacuate Athens, which was taken by the Persians, and seek the protection of their fleet. Subsequently, the Athenians and their allies, led by Themistocles, defeated the Persian navy at sea in the Battle of Salamis. Xerxes had built himself a throne on the coast in