View source for 421 BC

=== By place ===
==== Greece ====
* [[Nicias]], the leader of the aristocratic and peace party in [[Athens]] and [[Pleistoanax]], King of [[Sparta]], negotiate the [[Peace of Nicias]] between Athens and Sparta, which brings a temporary end to the [[Peloponnesian War]]. The essence of the Peace of Nicias is a return to the antebellum period with most wartime gains being returned. Seventeen representatives from each side swear an oath to uphold the treaty, which is meant to last for one generation (30 years: meaning they are not responsible for the next generation's decision). All of Sparta's allies agree to sign the peace except for the [[Boeotia]]ns, [[Ancient Corinth|Corinth]], [[Ancient Elis|Elis]], and [[Megara]].
* [[Alcibiades]] engineers an anti-Spartan alliance between Athens and the democracies of [[Argos, Peloponnese|Argos]], [[Mantinea]] and Elis.

==== Italy ====
* The city of [[Cumae]], the most northerly of the [[Ancient Greece|Greek]] colonies in [[Italy]], falls to the [[Samnites]].