The half century after the Persian Wars saw a change in the balance of power and political alignments in the Greek world. Athens emerged from the war as the strongest naval power in the Aegean and in the course of the following decades forged an empire with tributary territory in the Aegean, the mainland of Asia Minor and in Greece itself that made her one of the two great powers on the mainland. Her rival was Sparta, the preeminent Greek land power.

The latter’s strength lay in her own peculiar social system, in the military specialists she produced in a world of amateurs and in the Peloponnesian League whose military forces she controlled. By 431 the two rivals had clashed openly and in mobilizing their allies created a conflict on a scale that its historian Thucydides recognized dwarfed earlier wars between Greeks.

The prolonged and exhausting conflict, lasting with pauses from 431 to 404, was a watershed in Greek military, social and political history. The strength of the two protagonists and the length of the struggle transformed warfare from a seasonal activity to one in which at least low-scale conflict lasted throughout the traditionally inactive winter months. Low-level conflict was in fact characteristic of most of the war. Only two large hoplite battles were fought, Delium in 424 and First Mantinea in 418 during a formal lull in the war. There were also large-scale engagements by Athenian forces attacking Syracuse between 415 and 413 but for the most part the traditional decisive encounter did not take place. Much of the low-level activity on the Athenian side was in the nature of seaborne raids on the Peloponnese, and the war showed the limitations of traditional rules of conflict. Because of her dominance at sea and in fortifications Athens could allow enemy occupation of her land without abandoning her food supply, which could be transported from the Black Sea and other grain growing regions. The war also illustrated the limits of that seapower. It could be useful in stalemating an enemy overwhelmingly more powerful on land without being able to bring about a decisive result on its own.

The hard-line policies of Pericles (495–429), Athens’ most influential politician, helped bring Athens into the war. Now he had a plan for how the Athenians were going to survive. He knew that the Athenians were outnumbered and outclassed on land, but the Athenians did have huge advantages on the sea. The Athenians had 300 triremes, and with those of their free allies such as Corcyra, Chios, and Lesbos the number may have reached 500. Sparta had no ships of its own; its allies had maybe 100 triremes. As on land, there was a disparity not just in quantity but also in quality: the Athenian sailors were the best in the Mediterranean.

Therefore, the Athenians would not challenge Sparta in a land battle. Instead, most of the population of Attica, and at least some of their property, would be pulled back inside the Long Walls that connected the city of Athens to the harbor at the Piraeus, five miles away. In essence, Pericles intended to turn the city of Athens into an island, while the Athenian navy would protect Athenian control of the seas; this would allow the Athenians to import all the goods, especially food, they needed to survive. The navy would also maintain control of the empire, ensuring that the tribute necessary to finance their war effort, and especially the expensive navy, would continue to flow into the city. The navy would also be used to carry out offensive missions against the Peloponnesus and other enemy targets. Pericles’ defensive policy of course meant handing over most of Attica to Peloponnesian depredations, so restraining his own countrymen was going to be difficult, yet he hoped Athens could hold out for a few years until the Spartans finally realized that the war was pointless and gave up, in the process acknowledging Athens as an equal and recognizing the legitimacy of the Athenian Empire. Once the Spartans quit, Athens’ other enemies would not be able to fight on alone.

Both sides therefore believed they could achieve their strategic goals. However, as often happens in history, so many unforeseen factors intervene once war begins that conflicts rarely unfold as expected. To the great shock of the Greeks, at least to those who were still left alive in 404, it would take 27 years and much destruction and bloodshed before the Peloponnesian War came to an end.

The Naval Campaign: Peloponnesian War, 413–404

In 415, Athens made one of the great blunders of the war by attempting to conquer the island of Sicily. In 413, almost the entire Athenian expeditionary force was wiped out near the Sicilian city of Syracuse, leaving Athens with barely 10,000 hoplites and 100 triremes. The Syracusan disaster was only the beginning: between 413 and 410 Athens suffered numerous external and internal blows that nearly destroyed the city. The Spartans decided to renew the Peloponnesian War and invaded Attica in 413. For the first time, they built a permanent fort in Athenian territory at Decelea. Many subjects of the Athenian Empire now decided it would be a great time to rise up in rebellion. In 411, oligarchs in Athens, who had suffered the most economic losses because of the war, seized power and drove out the democrats. The Athenian fleet was at Samos at the time of the coup, and, since most of the sailors were lower-class Athenian citizens, they were not at all happy with the change in government. The sailors at Samos then declared that they represented the true government, the democratic government of Athens. So, on top of all the external crises, the Athenians were now literally divided.

In addition to these problems, what would prove in the long run to be the most dangerous threat to the Athenians was the sudden reappearance on the Greek stage of the ancient enemy Persia. By the Peace of Callias in 449, the Persians had essentially agreed to stay away from all Greek lands. Yet the Persians were not content with the new status quo, which gave Athens control of cities that had once belonged to the great king. So the Persians now saw an opportunity to bring down Athens by providing financial aid to its enemies. Persia would follow a similar strategy even after the Peloponnesian War had ended; when one Greek state became too powerful and potentially a threat to Persia, Persia would again intervene in Greek affairs by aiding those Greek states fighting against the growing power. In this way, with minimal effort, the Persians were able to help keep the Greeks weak and divided for nearly eight decades.

In the Peloponnesian War, the Persians intervened in Greek affairs on the side of the Spartans. Specifically, they provided funds to allow the Spartans to build a navy in return for Spartan assurances that in case of an Athenian defeat its subject cities in Asia would be turned over to Persia. Not surprisingly, Sparta kept this part of the bargain secret. Now, for the first time in the war, Sparta could challenge the Athenians on the sea. Previously, neither side could challenge the other in its position of strength, meaning that no decisive battle could be fought. Now the Spartan navy could challenge Athenians’ control of their empire and the trade routes that allowed Athens to survive the long blockade. More important, Persian money was nearly unlimited, meaning that even if the Spartans lost a fleet or even more than one, the Persians could provide more money to build replacements. The Second half of the Peloponnesian War would be very different from the first as the entire dynamic of the war had changed. The outcome would now be decided on the sea.