Battle of Plataea in the context of "Phlius"

The Delian League was a confederacy of Greek city-states, numbering between 150 and 330, founded in 478 BC under the leadership (hegemony) of Athens, whose purpose was to continue fighting the Persian Empire after the Greek victory in the Battle of Plataea at the end of the Second Persian invasion of Greece. The League functioned as a dual—offensive and defensive—alliance (symmachia) of autonomous states, similar to its rival association, the Peloponnesian League. The League's modern name derives from its official meeting place, the island of Delos, where congresses were held within the sanctuary of the Temple of Apollo; contemporary authors referred to the organization simply as "the Athenians and their Allies".

While Sparta excelled as Greece's greatest power on land, Athens turned to the seas, becoming the dominant naval power of the Greek world. Following Sparta's withdrawal from the conflict with Persia, Athens took the lead of the Hellenic alliance accompanied by several states around the Aegean and the Anatolian coast. The Delian League was formed as an anti-Persian defensive association of equal city-states seeking protection under Athens, as the latter wished to extend its support towards the Ionian Greek colonies of Anatolia. The alliance held an assembly of representatives in order to shape its policy, while members swore an oath of loyalty to the coalition. By the mid-fifth century BC, it had developed into a naval imperial power, conventionally called the Athenian Empire, where Athens established complete dominion and the allies became increasingly less autonomous. The League successfully accomplished its principal strategic goal by decisively expelling the remaining Persian forces from the Aegean. As a result, Persia would cease to pose a major threat to Greece for the following fifty years.

Herodotus (Ancient Greek: Ἡρόδοτος, romanized: Hēródotos; c. 484 – c. 425 BC) was a Greek historian and geographer from the Greek city of Halicarnassus (now Bodrum, Turkey), under Persian control in the 5th century BC, and a later citizen of Thurii in modern Calabria, Italy. He wrote the Histories, a detailed account of the Greco-Persian Wars, among other subjects such as the rise of the Achaemenid dynasty of Cyrus. He has been described as "The Father of History", a title conferred on him by the ancient Roman orator Cicero.

The Histories primarily cover the lives of prominent kings and famous battles such as Marathon, Thermopylae, Artemisium, Salamis, Plataea, and Mycale. His work deviates from the main topics to provide a cultural, ethnographical, geographical, and historiographical background that forms an essential part of the narrative and provides readers with a wellspring of additional information.

Hoplites (/ˈhɒplaɪts/ HOP-lytes) (Ancient Greek: ὁπλῖται, romanized: hoplîtai [hoplîːtai̯]) were citizen-soldiers of Ancient Greek city-states who were primarily armed with spears and shields. Hoplite soldiers used the phalanx formation to be effective in war with fewer soldiers. The formation discouraged the soldiers from acting alone, for this would compromise the formation and minimize its strengths. The hoplites were primarily represented by free citizens – propertied farmers and artisans – who were able to afford a linen or bronze armour suit and weapons (estimated at a third to a half of its able-bodied adult male population). Some states maintained a small elite professional unit, known as the epilektoi or logades ('the chosen') because they were picked from the regular citizen infantry. These existed at times in Athens, Sparta, Argos, Thebes, and Syracuse, among other places. Hoplite soldiers made up the bulk of ancient Greek armies.

In the 8th century BC, Greek armies started to adopt the phalanx formation. The formation proved successful in defeating the Persians when employed by the Athenians at the Battle of Marathon in 490 BC during the First Greco-Persian War. The Persian archers and light troops who fought in the Battle of Marathon failed because their bows were too weak for their arrows to penetrate the wall of Greek shields of the phalanx formation. The phalanx was also employed by the Greeks at the Battle of Thermopylae in 480 BC and at the Battle of Plataea in 479 BC during the Second Greco-Persian War.

The kingdom of Macedonia was an ancient state in what is now the Macedonian region of northern Greece, founded in the mid-7th century BC during the period of Archaic Greece and lasting until the mid-2nd century BC. Led first by the Argead dynasty of kings, Macedonia became a vassal state of the Achaemenid Empire of ancient Persia during the reigns of Amyntas I of Macedon (r. 547 – 498 BC) and his son Alexander I of Macedon (r. 498 – 454 BC). The period of Achaemenid Macedonia came to an end in roughly 479 BC with the ultimate Greek victory against the second Persian invasion of Greece led by Xerxes I and the withdrawal of Persian forces from the European mainland.

During the age of Classical Greece, Perdiccas II of Macedon (r. 454 – 413 BC) became directly involved in the Peloponnesian War (431–404 BC) between Classical Athens and Sparta, shifting his alliance from one city-state to another while attempting to retain Macedonian control over the Chalcidice peninsula. His reign was also marked by conflict and temporary alliances with the Thracian ruler Sitalces of the Odrysian Kingdom. He eventually made peace with Athens, thus forming an alliance between the two that carried over into the reign of Archelaus I of Macedon (r. 413 – 399 BC). His reign brought peace, stability, and financial security to the Macedonian realm, yet his little-understood assassination (perhaps by a royal page) left the kingdom in peril and conflict. The turbulent reign of Amyntas III of Macedon (r. 393 – 370 BC) witnessed devastating invasions by both the Illyrian ruler Bardylis of the Dardani and the Chalcidian city-state of Olynthos, both of which were defeated with the aid of foreign powers, the city-states of Thessaly and Sparta, respectively. Alexander II (r. 370 – 368 BC) invaded Thessaly but failed to hold Larissa, which was captured by Pelopidas of Thebes, who made peace with Macedonia on condition that they surrender noble hostages, including the future king Philip II of Macedon (r. 359 – 336 BC).

The helots (/ˈhɛləts, ˈhiːləts/; Greek: εἵλωτες, heílotes) were a subjugated group that constituted a majority of the population of Laconia and Messenia – the territories ruled by Sparta in Ancient Greece. There has been controversy since antiquity as to their exact characteristics, such as whether they constituted an Ancient Greek tribe, a social class, or both. For example, Critias described helots as "slaves to the utmost", whereas according to Pollux, they occupied a status "between free men and slaves". Tied to the land, they primarily worked in agriculture as a majority and economically supported the Spartan citizens.

The proportion of helots in relation to Spartan citizens varied throughout the history of the Spartan state; according to Herodotus, there were seven helots for each of the 5,000 Spartan soldiers at the time of the Battle of Plataea in 479 BC. Thus the need to keep the helot population in check and to prevent rebellion were major concerns of the Spartans. Helots were ritually mistreated and humiliated. Every autumn the Spartan polis declared war on the helots, allowing them to be killed and abused by members of the Crypteia without fear of religious repercussion. Uprisings and attempts to improve the lot of the helots did occur, such as the conspiracy of Cinadon of 399 BC. Plato on the other hand does not mention the killings by the Crypteia at all in Laws. The population was largely liberated by the Theban commander Epaminondas following the Theban-Spartan War.

The Battle of Mycale was one of the two major battles (the other being the Battle of Plataea) that ended the second Persian invasion of Greece during the Greco-Persian Wars. It took place on 27 or 28 August, 479 BC on the slopes of Mount Mycale, which is located on the coast of Ionia opposite the island of Samos. The battle was fought between an alliance of Greek city-states, including Sparta, Athens and Corinth; and the Persian Empire of Xerxes I.

The previous year, the Persian invasion force, led by Xerxes himself, had scored victories at the battles of Thermopylae and Artemisium, and conquered Thessaly, Boeotia and Attica; however, at the ensuing Battle of Salamis, the Greek navy had won an unlikely victory, and therefore prevented the conquest of the Peloponnese. Xerxes then retreated, leaving his general Mardonius with a substantial army to finish off the Greeks the following year.