Year 405 BC was a year of the pre-Julian Roman calendar.
|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:||408 BC 407 BC 406 BC – 405 BC – 404 BC 403 BC 402 BC|
- The Athenian fleet follows the Spartan admiral, Lysander, to the Hellespont. The Athenian fleet is destroyed in the Battle of Aegospotami.
- The Spartan king Pausanias lays siege to Athens. Lysander's fleet blockades Piraeus. This starves Athens.
- Theramenes tries to negotiate with Lysander. He is away for three months.
- Dionysius the Elder rises to power as the tyrant of Syracuse. He makes peace with the Carthaginian general. Carthage is in control of most of Sicily.
- Dionysius the Elder expands his power. He builds a wall around Syracuse. The Greek citizens of Naxos, Catana, and Leontini are removed from their cities. Many of them are made slaves.
- Aristophanes' play The Frogs is performed.
- Euripides' The Bacchae and Iphigeneia at Aulis are performed at the Dionysia and win first prize.
- The Erechtheum, which includes The Porch of Maidens (Caryatid Porch), is completed in the Ionian style on the Acropolis in Athens after 16 years of building.