The two Persian invasions, the first under Datis and Artaphernes (490 <small>B.C.</small>) in the reign of Darius I, the second by Xerxes in person (480-479 <small>B.C.</small>), had proved the need of closer co-operation among the Hellenic States, and the Delian League was formed under the leadership of Athens and with Athens as the “predominant partner.” An annual tribute was paid by all the member-states for the maintenance of a fleet. Athens was the treasurer and the fleet was mainly Athenian, while the commanders were entirely so. The power thus concentrated in Athens gave her so marked a supremacy that Pericles used the League to form an Athenian Empire. This lasted about thirty years (461-430 <small>B.C.</small>), during which period Athens reached the culmination not only of her power but also of her magnificence. For Pericles spent the money, contributed by the allies for common defence, in beautifying the Acropolis; the excuse being that in doing so he was giving glory to Athena, who was the patron goddess of the League. Pericles also encouraged literature and counted among his friends three of the greatest Greek writers--Sophocles, Herodotus, and Thucydides. But the power of Athens incited the envy of the other states, which ranged themselves with Sparta. In the Peloponnesian wars, the supremacy of Athens was broken and the Athenian Empire was succeeded by a Spartan Empire, which in time succumbed to the Theban Hegemony. Finally Hellas was conquered by Philip of Macedon and passed into the Macedonian Empire, established by this king and enlarged by his son, Alexander the Great. Through all these struggles Athens, though despoiled of her supremacy, played a big part until she was conquered by Philip at Chæronæa, in 338 <small>B.C.</small> The latter date is adopted as the end of the Great Age which had lasted since 480 <small>B.C.</small>, including within its circumference the age of Pericles. Besides its triumphant achievements in architecture and sculpture, the Great Age comprised in drama the names of Æschylus, Sophocles, Euripides, and Aristophanes; in history, Herodotus, Thucydides; in oratory, Demosthenes; in philosophy, Aristotle and Plato. Meanwhile, the century preceding it had produced, among the poets, Anacreon and Sappho; and, as representatives of mathematics, astronomy, geography, and metaphysics, Thales, Pythagoras, Xenophanes, Heraclitus, Parmenides, Anaximander, and Hecatæus of Miletus.