The oldest known human presence in Athens is the Cave of Schist, which has been dated to between the 11th and 7th millennium BC. Athens has been continuously inhabited for at least 7000 years. By 1400 BC the settlement had become an important centre of the Mycenaean civilization and the Acropolis was the site of a major Mycenaean fortress, whose remains can be recognised from sections of the characteristic Cyclopean walls. Unlike other Mycenaean centers, such as Mycenae and Pylos, it is not known whether Athens suffered destruction in about 1200 BC, an event often attributed to a Dorian invasion, and the Athenians always maintained that they were “pure” Ionians with no Dorian element. However, Athens, like many other Bronze Age settlements, went into economic decline for around 150 years afterwards. By the 6th century BC, widespread social unrest led to the reforms of Solon. These would pave the way for the eventual introduction of democracy by Cleisthenes in 508 BC. Athens had by this time become a significant naval power with a large fleet, and helped the rebellion of the Ionian cities against Persian rule. In the ensuing Greco-Persian Wars Athens, together with Sparta, led the coalition of Greek states that would eventually repel the Persians, defeating them decisively at Marathon in 490 BC, and crucially at Salamis in 480 BC. However, this did not prevent Athens from being captured and sacked twice by the Persians within one year, after a heroic resistance at Thermopylae by Spartans and other Greeks led by King Leonidas, after both Boeotia and Attica fell to the Persians. The decades that followed became known as the Golden Age of Athenian democracy, during which time Athens became the leading city of Ancient Greece, with its cultural achievements laying the foundations of Western civilization. The playwrights Aeschylus, Sophocles and Euripides flourished in Athens during this time, as did the historians Herodotus and Thucydides, the physician Hippocrates, and the philosopher Socrates. Guided by Pericles, who promoted the arts and fostered democracy, Athens embarked on an ambitious building program that saw the construction of the Acropolis of Athens (including the Parthenon), as well as empire-building via the Delian League. Originally intended as an association of Greek city-states to continue the fight against the Persians, the league soon turned into a vehicle for Athens’s own imperial ambitions. The resulting tensions brought about the Peloponnesian War (431–404 BC), in which Athens was defeated by its rival Sparta. By the mid-4th century BC, the northern Greek kingdom of Macedon was becoming dominant in Athenian affairs. In 338 BC the armies of Philip II defeated an alliance of some of the Greek city-states including Athens and Thebes at the Battle of Chaeronea, effectively ending Athenian independence. Later, under Rome, Athens was given the status of a free city because of its widely admired schools. The Roman emperor Hadrian, in the 2nd century AD, constructed a library, a gymnasium, an aqueduct which is still in use, several temples and sanctuaries, a bridge and financed the completion of the Temple of Olympian Zeus.