|Millennium:||1st millennium BC|
|412 BC by topic|
|Gregorian calendar||412 BC|
|Ab urbe condita||342|
|Ancient Egypt era||XXVII dynasty, 114|
|- Pharaoh||Darius II of Persia, 12|
|Ancient Greek era||92nd Olympiad (victor)¹|
|Balinese saka calendar||N/A|
|Chinese calendar||戊辰年 (Earth Dragon)|
2285 or 2225
— to —
己巳年 (Earth Snake)
2286 or 2226
|Coptic calendar||−695 – −694|
|Ethiopian calendar||−419 – −418|
|- Vikram Samvat||−355 – −354|
|- Shaka Samvat||N/A|
|- Kali Yuga||2689–2690|
|Iranian calendar||1033 BP – 1032 BP|
|Islamic calendar||1065 BH – 1064 BH|
|Minguo calendar||2323 before ROC|
|Thai solar calendar||131–132|
−285 or −666 or −1438
— to —
−284 or −665 or −1437
Year 412 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Ambustus and Pacilus (or, less frequently, year 342 Ab urbe condita). The denomination 412 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- The Persians under Darius II see their opportunity to play off one Greek city-state against another and to recover control of the Greek cities of Asia Minor, which have been under Athenian control since 449 BC. The satraps of Asia Minor, Tissaphernes and Pharnabazus, are ordered to collect overdue tribute.
- The Spartans sign a treaty of mutual help with the Persian satrap of Lower Asia, Tissaphernes. By the treaty of Miletus, Persia is given complete freedom in western Asia Minor in return for agreeing to pay for seamen to man the Peloponnesian fleet.
- Alcibiades helps stir up revolts amongst Athens' allies in Ionia, on the west coast of Asia Minor. However, Alcibiades loses the confidence of the Spartans and antagonises their king Agis II. As a result, he flees to the court of the Persian satrap Tissaphernes. Alcibiades advises Tissaphernes to withdraw his support from Sparta while conspiring with the oligarchic party in Athens, as Sparta's allied cities break away in a series of revolts.
- The Athenians vote to use their last reserves to build a new fleet.
- Clazomenae revolts against Athens. After a brief resistance, however, it again acknowledges the Athenian supremacy.
- An epidemic of an unknown disease hits Northern Greece.
- The epidemic hits the Roman Republic and causes a food shortage.
Diogenes of Sinope