The battle of Olynthus (381 BC) was the second battle fought by the Spartans close to the city during their expedition to Chalcidice, and ended with defeat and the death of the Spartan commander Teleutias.
In 382 both King Amyntas III of Macedon and the Chalcidian cities of Acanthus and Apollonia sent embassies to Sparta to ask for help against the rising power of Olynthus and her Chalcidian League. Sparta agreed to held, and sent an army north. This first army moved in two waves, but only the smaller advance guard reached Thrace, while the larger part got tangled in the politics of Thrace.
Later in the year the Spartans decided to send a second army north, under the command of Teleutias, a half brother of King Agesilaus. Teleutias gained a significant number of allies on the way north, including a contingent from Thebes, mercenaries from Macedon, and a force of Thracian cavalry under King Derdas of Elimia. His first attack on Olynthus nearly ended in defeat, before Derdas forced the Olynthians to retreat (battle of Olynthus, 382 BC). Although Teleutias claimed a victory, across the winter the Olynthians were able to conduct raids into enemy territory.
381 began with a success for the Spartans and their allies, when Derdas ambushed a Olynthian cavalry force that was raiding Apollonia, and pursued it back to Olynthus.
This was the high point of Spartan success in 381, but things were about to go badly wrong. Teleutias decided to conduct a fresh raid into Olynthian territory, probably without Derdas, who isn’t mentioned in Xenophon's account of the battle. Teleutias's aim was to destroy any remaining crops or fruit trees in Olynthian territory (presumably including the slow growing olive trees and the fig trees that Olynthus was named after). His army operated in the area on the opposite side of the River Sandanus, which ran right by the city walls.
The Olynthians had clearly not been too badly discouraged by the setback at Apollonia, and they sent their cavalry out to harass the Spartans. The cavalry crossed the river, and quietly approached the Spartan camp. Teleutias was angered by this, and ordered Tlemonidas and the light infantry to charge the Olynthian cavalry. The Olynthians withdrew, and re-crossed the river, luring Teleutias's light infantry into pursing them across the river. Once Teleutias's light infantry was vulnerable on the opposite side of the river to the rest of the army, the Olynthian cavalry turned back and attacked. Tlemondias and one hundred of his men were killed in this phase of the battle.
Teleutias responded to the sent back angrily. He led his hoplites towards the fighting, and ordered his peltasts and cavalry to pursue the Olynthians, who presumably chose to retire rather than risk a clash with the Spartan heavy infantry. The Olynthians retreated back into the city, with the Spartans in close pursuit.
This triggered the final stage of the battle. The Spartans came under heavy missile fire from the city walls, and were forced to pull back. While they were concentrating on protecting themselves against the missile fire, they were hit by another Olynthian cavalry charge, supported by their light infantry. The Olynthian heavy infantry was finally committed to the battle, catching Teleutias's men in some confusion. Teleutias himself was killed in the fighting, and the rest of his army then broke and fled. The army scattered into several directions, with parts fleeing north to Apollonia, other parts heading for Spartolus or Acanthus, and the largest part fleeing towards the Spartan base at Potidaea. The Olynthians mounted an effective pursuit. Both Xenophon and Diodorus record heavy losses during this battle, with Xenophon saying that the 'pith and kernel' of the army was lost, and Diodorus giving a figure of 1,200 Lacedaemonian dead.
The Spartans responded to this defeat by sending yet another army north, this time under the command of King Agesipolis. Agesipolis achieved very little during his time in the north, before dying of a fever in the summer of 380 BC. He was replaced by Polybiades, who was finally able to bring the war to an end, winning a series of poorly documented victories before besieging the city.