Demosthenes (Greek: Δημοσθένης, died 413 BC), son of Alcisthenes, was an Athenian general during the Peloponnesian War.

The military activities of Demosthenes are first recorded from 426 BC when he led an Athenian invasion of Aetolia.

The Acarnanians sought help from Demosthenes, who was now patrolling the coast of the Ionian Sea with twenty Athenian ships.

[6] In order to keep busy, his soldiers impulsively fortified the promontory, which was Demosthenes' wish however he had failed to persuade the other generals.

After Athens invaded Sicily in 415 BC, a Spartan fleet arrived to reinforce their allies in Syracuse, with a stalemate ensuing.

After initial success, the Athenians became disorganized in what became a chaotic night operation, and were thoroughly routed by Gylippus, the Spartan commander.

After the defeat, and upon seeing the disease-ridden Athenian camp, Demosthenes suggested that they immediately give up the siege and return to Athens, where they were needed to defend the city against a Spartan invasion of Attica.

The delay allowed the Syracusans and Spartans to trap the Athenian forces in the harbour and Eurymedon was killed in the ensuing battle.