Prelude

As the preeminent Athenian historian, Thucydides, wrote in his influential History of the Peloponnesian War, "The growth of the power of Athens, and the alarm which this inspired in Lacedaemon, made war inevitable."^[4] Indeed, the nearly fifty years of Greek history that preceded the outbreak of the Peloponnesian War had been marked by the development of Athens as a major power in the Mediterranean world. Its empire began as a small group of city-states, called the Delian League — from the island of Delos, on which they kept their treasury — that came together to ensure that the Greco-Persian Wars were truly over. After defeating the Persian invasion of Greece in the year 480 BC, Athens led the coalition of Greek city-states that continued the Greco-Persian Wars with attacks on Persian territories in the Aegean and Ionia. What then ensued was a period, referred to as the Pentecontaetia (the name given by Thucydides), in which Athens increasingly came to be recognized as an Athenian Empire,^[5] carrying out an aggressive war against Persia. After a time, though, Athens' influence began to dominate the other city-states. The city proceeded to conquer all of Greece save for Sparta and its allies, and became known as the Athenian Empire. By the middle of the century, the Persians had been driven from the Aegean and forced to cede control of a vast range of territories to Athens. At the same time, Athens greatly increased its own power; a number of its formerly independent allies were reduced, over the course of the century, to the status of tribute-paying subject states of the Delian League. This tribute was used to support a powerful fleet and, after the middle of the century, to fund massive public works programs in Athens, ensuring resentment.^[6]

Friction between Athens and Peloponnesian states, including Sparta, began early in the Pentecontaetia; in the wake of the departure of the Persians from Greece, Sparta attempted to prevent the reconstruction of the walls of Athens (without the walls, Athens would have been defenseless against a land attack and subject to Spartan control), but was rebuffed.^[7] According to Thucydides, although the Spartans took no action at this time, they "secretly felt aggrieved".^[8] Conflict between the states flared up again in 465 BC, when a helot revolt broke out in Sparta. The Spartans summoned forces from all of their allies, including Athens, to help them suppress the revolt. Athens sent out a sizable contingent (4,000 hoplites), but upon its arrival, this force was dismissed by the Spartans, while those of all the other allies were permitted to remain. According to Thucydides, the Spartans acted in this way out of fear that the Athenians would switch sides and support the helots; the offended Athenians repudiated their alliance with Sparta.^[9] When the rebellious helots were finally forced to surrender and permitted to evacuate the country, the Athenians settled them at the strategic city of Naupactus on the Corinthian Gulf.^[10]

In 459 BC, Athens took advantage of a war between its neighbors Megara and Corinth, both Spartan allies, to conclude an alliance with Megara, giving the Athenians a critical foothold on the Isthmus of Corinth. A fifteen-year conflict, commonly known as the First Peloponnesian War, ensued, in which Athens fought intermittently against Sparta, Corinth, Aegina, and a number of other states. For a time during this conflict, Athens controlled not only Megara but also Boeotia; at its end, however, in the face of a massive Spartan invasion of Attica, the Athenians ceded the lands they had won on the Greek mainland, and Athens and Sparta recognized each other's right to control their respective alliance systems.^[11] The war was officially ended by the Thirty Years' Peace, signed in the winter of 446/5 BC.^[12]