The Battle of Chalcis took place in 429 BC between Athens and the Chalcidians and their allies, in the early part of the Peloponnesian War.
The Athenians under Xenophon marched into Thrace to attack Chalcis. They destroyed the crops outside Spartolus and began negotiating with pro-Athenian factions in Chalcis, but the anti-Athenian factions asked for help from Olynthus. An army from Chalcis, Spartolus, and Olynthus met the Athenians in battle, but their hoplites were defeated and they retreated to Spartolus; their cavalry, however, was victorious against the Athenian troops. Reinforcements soon arrived from Olynthus, and they launched a second attack on the Athenians. The Athenians panicked and were routed, with all of their generals and 430 other men killed.