Alcidas, the Spartan commander sent to assist…

The Spartan conquerors of Plataea, on the other hand, have no such doubters among them.

When the remaining Plataeans surrender (some had already broken out to Athens) in 427, the Spartans put them to death to a man, after posing the “brief question”, “Have you done anything for Sparta during the war?”

Thebes takes over Plataea's vote in the Boeotian League and some of its territory after the destruction of the city in 427 BCE.

Civil strife occurs at Corcyra when, after a bloodbath in 427 BCE, the democratic pro-Athenian faction prevails over the oligarchical pro-Spartan party, with the Athenian commander Eurymedon not attempting to stop it.

The enslaved people, promised freedom by both sides, go over to the democrats (who may simply have made better offers).

Athens mounts a vain attempt by the Athenian general Nicias to take Megara by military means in 427, then ...

…seizes all but one base in the Gulf of Corinth.

Naxos allies with …

…Leontini in opposition to …

…Syracuse in 427 BCE.

Possibly, even the Spartans are uneasy at what the main events of 427, at Mytilene and Plataea, have done for their image: they have been ineffective and brutal.

Perhaps in partial redress, but also in pursuit of a traditional line of policy, they issue a general invitation to participate in a large (ten thousand strong) colony at Heraclea in Trachis at the southern approach to Thessaly.

This colonizing effort has intelligible short-term military motives, namely, a perceived need to gain a hold on the Thracian region—the only part of the Athenian empire reachable by land-and a desire to deny Athens access to its larder on Euboea.

However, Thessaly has always featured and is always to feature in ambitious Spartan thinking; and Sparta may already have designs on the amphictyonic vote that one certainly finds Heraclea exercising in the fourth century.

By excluding Ionians, Achaeans, and some others, Sparta is presenting itself as a leader of Dorians, not just as a selfish promoter of Spartan interests.

This is the redress offered to a Greek world well disposed toward Sparta at the beginning of the war but now perhaps dismayed by the way things are going.

Unfortunately, the brutality of Spartan governors at Heraclea, who are harsh and unjust, frightens people away and helps to ruin the project.

Athens' magnificent refounding, also in 426 BCE, of the Ionian festival of Apollo on the island of Delos, where the Delian League had been established in 478 BCE is surely in part a response to Dorian Heraclea. (Additional motives include desire for expiation for the plague, which in the winter of 427-426 BCE has ravaged Athens a second time.)

Of the two great Panhellenic sanctuaries, Olympia in 428 BCE had taken an ugly anti-Athenian look, while the oracle of Delphi had actually approved the Heraclea colony.

Athens, through Delos, is creating or inflating religious propaganda possibilities of its own.

The same is true of an Athenian invitation to the Greeks at large, also (possibly) in the 420s BCE, to bring offerings of first fruits to Eleusis.