- After suffering a defeat in which the Athenian commander Lamachus is killed, Demosthenes suggests that they immediately give up the siege of Syracuse and return to Athens, where they are needed to defend against a Spartan invasion of Attica. Nicias refuses, but the Syracusans and Spartans under Hermocrates are able to trap the Athenians in the harbour and the Athenians sustain heavy losses in the Battle of Syracuse. Demosthenes is ambushed by the Syracusans and is forced to surrender. Nicias is soon captured as well, and both are executed, with most of the surviving Athenian soldiers sent to work in the Sicilian quarries.
- Tissaphernes, the Persian satrap of Lydia and Caria, forms an alliance with Sparta. The Spartans, with strategic advice from Alcibiades and limited assistance from the Persians under Pharnabazus, advance almost to the gates of Athens. King Agis II leads the Spartan force that occupies Decelea in Attica.
- Archelaus I becomes King of Macedonia following the death of his father, King Perdiccas II. Archelaus seizes the throne after murdering his uncle, his cousin, and his half brother, the legitimate heir.