the east and southeast, and also the Arcadian Achaeans to the northwest. The evidence suggests that Sparta, relatively inaccessible because of the topography of the Taygetan plain, was secure from early on: it was never fortified. Nothing distinctive in the archaeology of the Eurotas River Valley identifies the Dorians or the Dorian Spartan state. The prehistory of the Neolithic, the Bronze Age and the Dark Age (the Early Iron Age) at this moment must be treated apart from the stream of Dorian Spartan history. The legendary period of Spartan history is believed to fall into the Dark Age. It treats the mythic heroes such as the Heraclids and the Perseids, offering a view of the occupation of the Peloponnesus that contains both fantastic and possibly historical elements. The subsequent proto-historic period, combining both legend and historical fragments, offers the first credible history. Between the 8th and 7th centuries BC the Spartans experienced a period of lawlessness and civil strife, later attested by both Herodotus and Thucydides. As a result, they carried out a series of political and social reforms of their own society which they later attributed to a semi-mythical lawgiver, Lycurgus. Several writers throughout antiquity, including Herodotus, Xenophon, and Plutarch have attempted to explain Spartan exceptionalism as a result of the so-called Lycurgan Reforms.Xenophon, Constitution of the Lacedaimonians, chapter 1 Classical Sparta In the Second Messenian War, Sparta established itself as a local power in the Peloponnesus and the rest of Greece. During the following centuries, Sparta's reputation as a land-fighting force was unequalled. At its peak around 500 BC, Sparta had some 20,000–35,000 citizens, plus numerous helots and perioikoi. The likely total of 40,000–50,000 made Sparta one of the larger Greek city-states; however, according to Thucydides, the population of Athens in 431 BC was 360,000–610,000, making it much larger. In 480 BC, a small force led by King Leonidas (about 300 full Spartiates, 700 Thespians, and 400 Thebans, although these numbers were lessened by earlier casualties) made a legendary last stand at the Battle of Thermopylae against the massive Persian army, led by Xerxes. The Spartans received advance warning of the Persian invasion from their deposed king Demaratus, which prompted them to consult the Delphic oracle. According to Herodotus, the Pythia proclaimed that either one of the kings of Sparta had to die or Sparta would be destroyed. This prophecy was fulfilled after king Leonidas died in the