|Millennium:||1st millennium BC|
|Centuries:||6th century BC – 5th century BC – 4th century BC|
|Decades:||430s BC 420s BC 410s BC – 400s BC – 390s BC 380s BC 370s BC|
|Years:||411 BC 410 BC 409 BC – 408 BC – 407 BC 406 BC 405 BC|
|408 BC by topic|
|Gregorian calendar||408 BC|
|Ab urbe condita||346|
|Ancient Egypt era||XXVII dynasty, 118|
|- Pharaoh||Darius II of Persia, 16|
|Ancient Greek era||93rd Olympiad (victor)¹|
|Chinese calendar||壬申年 (Water Monkey)
2289 or 2229
— to —
癸酉年 (Water Rooster)
2290 or 2230
|Coptic calendar||−691 – −690|
|Ethiopian calendar||−415 – −414|
|- Vikram Samvat||−351 – −350|
|- Shaka Samvat||N/A|
|- Kali Yuga||2694–2695|
|Iranian calendar||1029 BP – 1028 BP|
|Islamic calendar||1061 BH – 1060 BH|
|Minguo calendar||2319 before ROC
|Thai solar calendar||135–136|
|Wikimedia Commons has media related to 408 BC.|
Year 408 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Tribunate of Iullus, Ahala and Cossus (or, less frequently, year 346 Ab urbe condita). The denomination 408 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.
- King Darius II of Persia decides to continue the war against Athens and give support to the Spartans. His wife, Parysatis, persuades him to appoint his younger son, Cyrus, as satrap (governor) of Lydia, Phrygia, and Cappadocia and commander in chief of the Achaemenian forces in Asia Minor in place of Tissaphernes.
- Tissaphernes' influence is limited to the satrapy of Caria. Darius II also gives Cyrus funds to re-create the Spartan fleet and sends him to Sardis with instructions to increase Persian support for Sparta. Cyrus begins to collect an army of mercenaries (including Greeks) for his own ends.
- Alcibiades enters Athens in triumph after an absence of 7 years. He leads the religious procession from Athens to Eleusis, thus atoning for his alleged impiety in 415 BC when he was held to have joined in profaning the Sacred Mysteries. Alcibiades is appointed commander-in-chief with autocratic powers and leaves for Samos to rejoin his fleet.
- The Spartan admiral Lysander arrives at Ephesus in autumn and builds up a great fleet with help from the new Persian satrap, Cyrus.
- At the Panhellenic gathering at Olympia, the philosopher Gorgias speaks out against the Spartan alliance with Persia.
- Euripides' plays Orestes and The Phoenician Women are performed. Euripides then leaves Athens in dissatisfaction and travels to the court of Archelaus I of Macedon at the King's invitation.
- Eudoxus of Cnidus, Greek astronomer, mathematician, physician, scholar and adherent of Pythagoras (d. c. 355 BC)
- Dion, tyrant of Syracuse (d. c. 354 BC)