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.

The Ionians, who worshiped Dionysus, were the first to settle on the island of Myconus, one of the smaller of the eastern Cyclades; the Athenians in 426 BCE transfer the remains of the dead buried at the shrine on Delos to Rheneía, near Míkonos.

Land operations in the northwest occupy much of the purely military history of 426.

The Athenian Demosthenes, one of the finest generals of the Peloponnesian War, is at first spectacularly unsuccessful in some ambitious campaigning, perhaps not sanctioned by the Assembly at all, in Aetolia, where his hoplites are nearly helpless against the light-armed tactics of the locals, and …

…in the western islands, where he unsuccessfully besieges the Corinthian colony of Leukas.

Demosthenes redeems these failures by successfully defending Naupactus, the Athenian naval base in the Gulf of Corinth, against a Spartan land attack and …

…by winning two decisive victories over the Spartans, at Olpae near Argos and …

…at Idomene in the hills to the north of Argos.

Sparta does not attack Attica in 426 BCE, giving the Athenians their first break in three years.

Euripides had written another patriotic play, Andromache, around 426 BCE, and writes Hecuba, another of his plays of passion and revenge, about a year later.

Five years into the Peloponnesian war, Athenian playwright Aristophanes lays bare his own predilections in The Acharnians, produced in 425 BCE: the play’s protagonist, Just City, concludes a private and advantageous peace with Sparta.

The Temple of Athena Nike on the Acropolis, executed around 427 BCE, epitomizes the delicate, graceful decorative effects of the Ionic order.

Callimachus of Athens, according to Vitruvius is in 425 BCE the first to use the acanthus leaf on the new Corinthian capital design.