The Battle of Mantinea took place in 418 BC between Sparta and its allies, and an army led by Argos and Athens.

Battle of Mantinea
ConflictPeloponnesian War
Date418 BC
ResultSpartan victory
Agis II
About 4200Slightly less
About 300About 1100
In 418 Agis II, one of the Kings of Sparta, made a truce with Argos rather than conquering it. This was a very unpopular decision, and Agis was on the verge of being overthrown, but he promised a victory elsewhere. Agis marched out to Tegea where he was joined by his allies from Arcadia, and he sent for help from Corinth, Boeotia, Phocis, and Locria. They invaded the territory around Mantinea, near Argos, and drew up against the Argive army, but Agis retreated rather than risk battle. The Spartans went off to find a water supply, while the Argives marched out to a field near a Temple of Heracles, where they surprised the Spartans the next day. The Spartans quickly organized themselves, with no time to wait for their other allies. Brasidas (apparently not the same general who had been killed at the Battle of Amphipolis), the Thracians, and the Sciritae (an elite unit of Spartan troops) formed the left wing, the Spartans, Arcadians, and Maenalians in the centre, and the Tegeans on the right wing. The Argive lines were formed by the Mantineans on the right, the Argives in the centre, and the Athenians on the left. Thucydides did not know the exact numbers of men on each side, but estimated that there were about 4200 men on the Spartan side, with somewhat fewer men on the Argive and Athenian side.

As the battle began, each side's right wing began to outflank the other's left, due to the erratic movements of each hoplite trying to cover himself with the shield of the man beside him. Agis tried to strengthen the line by moving the troops under Brasidas, Hipponoidas, and Aristocles, but they were unable to complete these manoeuvres on such short notice. The Mantineans rushed into the gap created by these movements, but Agis defeated the Argives and Athenians, who fled almost immediately. The Mantineans stopped their attack and retreated when they saw the Argives and Athenians had been defeated. The Argive side lost about 1100 men, and the Spartans about 300.

The next year another truce was signed with Argos and Athens, designed to last for fifty years, and the Spartans and Argives began to ally with each other against other states.