Athens - Sparta War through Thebes' Liberation

In 379 B.C., the city of Thebes underwent a sudden and dramatic transformation that reshaped Greek affairs and triggered a renewed conflict between Athens and Sparta. Spartan dominance had seemed secure after the King’s Peace (Peace of Antalcidas), yet within a short span, the factional politics of both Thebes and Sparta—and ultimately Athens—set the stage for a new war. This post revisits the key events between 379 and 378 B.C. to show how Thebes liberated itself from Spartan control, how Sparta’s reaction unfolded through factional rivalry, and how the Athenians, initially hesitant, soon found themselves forming a new confederacy that challenged Spartan power.

Background

After the Corinthian War ended in 387 B.C. with the King’s Peace (or Peace of Antalcidas), Sparta was widely recognized as the hegemon of mainland Greece. Under King Agesilaus, she systematically reinforced her influence by:

• Installing or supporting pro-Spartan oligarchic factions in key cities (like Thebes).
• Placing Spartan garrisons where needed, including on the citadel of Thebes (the Cadmeia).
• Checking any rising powers like Olynthus in northeastern Greece.

In Athens, a more conservative faction, often associated with the figure Callistratus of Aphidna, preferred accommodation with Sparta and avoided challenging her dominance on land. Athens did cautiously expand maritime influence—particularly securing grain routes in the Aegean and the Black Sea—but did so in ways that did not provoke Sparta. Meanwhile, Thebes remained under a Spartan-backed government led by Leontiades, with a Spartan garrison stationed in the Cadmeia, ensuring that Theban affairs aligned with Spartan interests.

A Coup in Thebes

Within Thebes, however, an anti-Spartan faction in exile at Athens waited for an opportunity to recapture the city. In the winter of 379/378 B.C., one of the exiles, Melon, conspired with certain Thebans inside the city who despised the pro-Spartan rule of Leontiades. Initially, Athens did not officially endorse this plan—support came informally from a few Athenians, including two generals who discreetly positioned troops near the Attic–Boeotian border.

1. Thebes Reclaimed: Slipping into Thebes by night, the exiles assassinated key oligarchs, rallied other Thebans eager to shake off Spartan control, and quickly seized power. The Spartan garrison in the Cadmeia, outnumbered and cut off, surrendered on terms.
2. Uncertain Athenian Involvement: According to Xenophon, while Athenian volunteers did help after the Theban exiles’ victory, the city of Athens itself had not formally authorized this coup. Indeed, Athens later executed or exiled the two generals involved, to avoid Spartan reprisals.

Initially, Thebes sent ambassadors to Sparta, perhaps hoping for a compromise that recognized the new (anti-Spartan) government. But King Agesilaus and his allies demanded that the anti-Spartan faction be expelled—a demand Thebes refused.

Cleombrotus’ Failed Invasion (Early 378 B.C.)

Sparta responded militarily. Rather than lead the army himself, Agesilaus stepped aside, allowing his co-king Cleombrotus (brother of the late King Agesipolis) to command the campaign. This choice reflected Sparta’s internal factionalism:

• Agesilaus had used harsh methods outside the Peloponnese (e.g., interfering in Theban affairs). But after the Theban exiles’ success, critics could blame him for mismanaging policy.
• Cleombrotus might have wanted a more conciliatory approach—his family had sometimes pursued gentler methods with allies. Possibly he also saw an invasion of Boeotia as an opportunity to bolster his prestige at Agesilaus’ expense.

Cleombrotus’ Campaign in Boeotia:

He marched from Plataea to Thespiae, then lingered for about sixteen days at Cynoscephalae. Rather than crushing Thebes, he did almost nothing and withdrew. Xenophon says Spartan troops were puzzled whether there was war at all. Possibly Cleombrotus hoped Thebes would open negotiations, letting him forge a personal alliance there that might undermine Agesilaus’ standing. When Thebes refused, Cleombrotus accomplished nothing.

Seeds of Spartan–Athenian Discord

Even though Athens had tried to appease Sparta by punishing the two generals involved in the Theban coup, Spartan suspicions lingered. Meanwhile, Athens became anxious as a Spartan army hovered in Boeotia. To reassure Sparta that Athens was not waging an undeclared war, Athenians stationed a force on the border, under Chabrias, to guard against potential incursions—but not to openly attack Sparta’s forces.

1. Spartan Ambassadors to Athens: While Cleombrotus tarried in Boeotia, Sparta also sent ambassadors (including Etymocles, an ally of Agesilaus) to Athens. They presumably demanded the state punish the pro-Theban generals, or at least reaffirm peaceful ties.
2. Athenian Compliance: With the conservative group of Callistratus still in charge, Athens indeed tried to keep the peace. The city condemned one general to death and exiled the other. Thus Athens seemed to remain “neutral” about Thebes, not wanting to provoke a direct war with Sparta.

The Sphodrias Affair

Shortly afterward, Sphodrias, a Spartan harmost left with a considerable force at Thespiae by Cleombrotus, made a sudden night march on Peiraeus (the port of Athens), hoping to seize it by surprise. If successful, this move would have crippled Athens’ naval power at its very core.

• Motives and Factional Politics:
  • Xenophon accuses Theban gold of bribing Sphodrias, but this is almost certainly implausible. The real driving force seems to be within Sparta itself.
  • Cleombrotus, having failed to subdue Thebes, may have sanctioned Sphodrias’ raid to redeem his standing in Sparta. By capturing Peiraeus, he would remove the “Athenian threat” and win favor among Spartans who wanted Aegean adventures reminiscent of Lysander’s policy.
  • If Sphodrias succeeded, Athens would be intimidated or forced into submission, leaving Thebes without a powerful ally.

Sphodrias underestimated distances or encountered bad weather. His troops fell behind schedule, and by dawn, they were still far from Peiraeus. Exposed, they retreated amid widespread outrage in Athens over this unprovoked aggression.

Athenian Fury and the Collapse of Pro-Spartan Factions

The Sphodrias affair galvanized Athenian public opinion against Sparta. Even though Spartan ambassadors in Athens pleaded ignorance, the Athenians, previously on the fence, now believed Sparta intentionally violated peace. The crisis left Callistratus’ pro-Spartan faction in disarray:

• Awaiting a Spartan Verdict: Initially, Athens refrained from an immediate declaration of war to see if Sparta would condemn Sphodrias. If he were severely punished, perhaps peace could still be salvaged.
• Spartan Dilemma: Sphodrias was recalled for trial. But deciding his fate fell into the tangle of Spartan factional politics:
  • Agesilaus initially seemed poised to punish him.
  • Cleombrotus’ supporters, however, championed Sphodrias.
  • In the end, Agesilaus, not wanting to strengthen Cleombrotus if Sphodrias was found guilty, chose to acquit him.

Result: When news reached Athens that Sphodrias was vindicated, the Athenians, enraged by Spartan duplicity, swung decisively toward war. A pro-Theban, anti-Spartan faction took over, reversing Callistratus’ policy.

Birth of the Second Athenian Confederacy (378 B.C.)

Once Athens recognized that Sparta would not punish Sphodrias, the city formally abandoned its stance of neutrality and prepared for open conflict. Several developments followed quickly:

1. Alliance with Thebes: Where Athens had previously hesitated to fully support Thebes, now it concluded Thebes’ aid on land was essential for countering Sparta.
2. Wider Invitations to Allies: Athens reached out to old and new potential friends, emphasizing autonomy and equality—unlike the oppressive Delian League of the fifth century.
3. Common Council: According to Diodorus, a synedrion was established in Athens with each allied state, large or small, having one vote. This formed the basis of what is called the Second Athenian Confederacy or League.
4. Military Preparedness: Under new leadership—Timotheus, Chabrias, and (ironically) Callistratus handling finances—Athens raised troops, built ships, and “closed” Peiraeus with gates.

Although Diodorus jumbles some details chronologically, there is no doubt that the Sphodrias affair was the catalyst pushing Athens into a firm alliance with Thebes and an expanded confederacy across the Aegean. In a matter of months, Sparta, having expected an easy reassertion of its mainland rule, now faced a formidable alliance of Thebes and Athens. The fragile Peace of Antalcidas had collapsed.

Repercussions and the Road to Larger War

By mid- to late 378, the factions in Athens favoring a defensive, pro-Spartan stance were marginalized. Athens committed to waging war on two fronts: (1) supporting Thebes on land, (2) reclaiming a broader naval presence in the Aegean that threatened Spartan influence in maritime affairs.

Over in Sparta:

• Agesilaus regained prominence, as the Spartans, angered by Athens’ new hostility, entrusted him again with their army to fight Thebes. His plan of controlling the mainland, curbing Thebes, and isolating Athens had a renewed chance of success—yet it also risked plunging Sparta into prolonged conflict that demanded considerable resources and exposed her to further rebellion.

In the immediate future, both sides would engage in repeated campaigns and naval expeditions. The conflict would drag on until the 370s, culminating in major realignments—most famously, Thebes’ dramatic ascendancy under Epaminondas and the defeat of Sparta at Leuctra in 371 B.C.

Conclusion

In sum, the liberation of Thebes from its Spartan-backed oligarchs was itself a potent symbol of anti-Spartan resurgence. But not until the Sphodrias affair—an attempted surprise assault on Peiraeus—did Athens fully mobilize against Sparta. This failed raid ignited Athenian outrage, discredited pro-Spartan politicians, and led directly to the creation of the Second Athenian Confederacy, a league that challenged Spartan supremacy far beyond Boeotia.

The year 379/378 B.C. thus stands out as a pivotal turning point. A single miscalculated night march orchestrated by a Spartan harmost named Sphodrias tipped the delicate balance of Greek politics, ended the post-Corinthian War peace, and opened a new chapter of conflict in which Thebes and Athens would become staunch allies. Within a few short years, Sparta’s long-held hegemony would be irreversibly weakened, paving the way for Thebes’ brief but astonishing ascent—and reshaping the Greek political landscape for decades to come.