Delian League

The Delian League was an alliance of Greek city-states, ranging from 150 to 330 members, established in 478 BC with Athens as its leading power. Its goal was to keep fighting the Persian Empire following the Greek triumph at Plataea, which ended the Second Persian Invasion. The League was a dual-purpose alliance—both offensive and defensive—made up of independent states, much like its Spartan-led rival, the Peloponnesian League. Its name comes from the island of Delos, where meetings took place at the Temple of Apollo’s sanctuary; people at the time simply called it "the Athenians and their Allies."

Athens, already a naval powerhouse, took charge after Sparta stepped back from the war with Persia, gathering support from states around the Aegean and Anatolian coast. The League began as a defensive pact of equal city-states seeking Athens’ protection, especially for Ionian Greek colonies in Anatolia. Members held an assembly to decide policy and swore loyalty to the coalition. By the mid-5th century BC, it had turned into a naval empire—often called the Athenian Empire—where Athens held total control and allies lost much of their independence. Under Cimon, the League achieved its main goal by driving Persian forces out of the Aegean, keeping Persia from threatening Greece for about fifty years.

From the start, Athens provided most of the League’s military strength, while more allies chose to pay their dues in cash. Athens then used these funds for its own ends, like boosting its navy, which sparked conflicts with weaker allies and sometimes rebellions, such as Thasos in 465 BC. The League’s treasury was originally on Delos, but Pericles moved it to Athens in 454 BC as a symbolic act. By 431 BC, the League’s threat to Spartan power, along with Athens’ heavy-handed rule, triggered the Peloponnesian War; the League was dissolved at the war’s end in 404 BC under Lysander’s direction. Seeing Sparta’s growing dominance in the early 4th century BC, Athens partly revived the alliance as the Second Athenian League, regaining naval control in the eastern Mediterranean.

**Background**

The Greco-Persian Wars started with Persia’s conquest of Greek cities in Asia Minor, especially Ionia, after 550 BC under Cyrus the Great. The Persians struggled to govern the Ionians, eventually placing a tyrant in each city. Though Greek states had often been ruled by tyrants, this system was fading. By 500 BC, Ionia was ready to rebel against these Persian-backed rulers. The tension erupted into open revolt when Aristagoras, the tyrant of Miletus, tried to save himself after a failed Persian expedition in 499 BC by declaring Miletus a democracy. This sparked similar uprisings across Ionia, Doris, and Aeolis, starting the Ionian Revolt.

Athens and Eretria got involved after Aristagoras asked for help, and during their only campaign season (498 BC), they helped capture and burn the Persian regional capital, Sardis. The revolt continued for five more years without outside aid, until the Persians crushed it. But King Darius the Great decided that, despite ending the revolt, he still needed to punish Athens and Eretria for their support. The revolt had shaken his empire, and mainland Greek states remained a threat unless dealt with. So Darius planned to conquer Greece, starting with destroying Athens and Eretria.

Over the next twenty years, two Persian invasions of Greece occurred, producing some of history’s most famous battles. In the first invasion, Persia added Thrace, Macedon, and the Aegean Islands to its empire and destroyed Eretria. But it ended in 490 BC with Athens’ decisive victory at Marathon. After that, Darius died, and his son Xerxes I took over the war. Xerxes led a second invasion in 480 BC with a huge army and navy. The Greek allies who resisted were beaten at the simultaneous battles of Thermopylae on land and Artemisium at sea. Most of Greece, except the Peloponnesus, fell to Persia. The Persians then tried to destroy the allied navy but lost badly at Salamis. The next year, 479 BC, the allies gathered the largest Greek army ever and defeated the invasion at Plataea, ending the threat to Greece. The allied fleet also defeated the remaining Persian fleet at Mycale near Samos—traditionally on the same day as Plataea—marking the end of the Persian invasion.