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The [[Athens |Athenians]] under Xenophon march into [[Thrace]] to attack [[Chalcis]]. They destroy crops outside [[Spartolus]] and begin negotiating with pro- Athenian factions in Chalcis, but the anti- Athenian factions ask for help from [[Olynthus]]. An army from Chalcis, Spartolus, and Olynthus meet the Athenians in [[ Battle of Chalcis| battle]], but their [[ hoplites]] are defeated. Reinforcements soon arrive from Olynthus , and they launch a second attack on the Athenians. The Athenians are routed, with all of their generals and 430 other men killed.
The Athenian admiral [[Phormio]] has two naval victories at [[ Battle of Naupactus (429 BC)|Naupactus]] at the mouth of the [[ Corinthian Gulf]]. In the first battle, his 20 ships defeat 47 [[Corinth]] ian ships commanded by [[Machaon]], [[Isocrates of Sparta|Isocrates]], and [[Agatharchidas]] that were advancing to reinforce the [[ Sparta]] n general, [[Cnemus]] ’ campaign in [[ Acarnania]] . In the second battle, Phormio routs Cnemus’ 77 -vessel fleet.
Macedonian king, [[Perdiccas II]], once again betrays the Athenians and sends 1000 troops to support a Spartan assault on [[Acarnania]] but they arrive too late to help. In response to this, King [[Sitalkes]] of [[Thrace]] invades [[Macedon |Macedonia]] with a vast army that includes independent Thracian tribes (such as the [[Dii]]) and [[Paionia |Paionian]] tribes ([[ Agrianes]], [[ Laeaeans]]). His progress is slowed when the promised support from [[Athens]] fails to materialise. So Perdiccas once again uses diplomacy to ensure the survival of Macedonia. He promises the hand of his sister in marriage to the nephew of Sitalkes , who then persuades Sitalkes to leave Macedonia.
The [[ Plague of Athens| plague]] in Athens that is killing thousands of the city's inhabitants, claims [[Pericles]]. [[Cleon]], who has headed the opposition to Pericles’ rule, succeeds to power in Athens following Pericles’ death.