Callimachus /kəˈlɪməkəs/ (Ancient Greek: Καλλίμαχος, romanized: Kallímakhos) was the Athenian polemarch at the Battle of Marathon, which took place during 490 BC. According to Herodotus, he was from the Attica deme of Aphidna.

As polemarch, Callimachus had a vote in military affairs along with the 10 strategoi, including Miltiades. Miltiades convinced Callimachus to vote in favour of a battle when the strategoi were split evenly on the matter.

Miltiades is supposed to have said to Callimachus just before the polemarch cast his vote: "Everything now rests on you."^{[citation needed]}

During the battle, as polemarch, Callimachus commanded the right wing of the Athenian army as was the Athenian custom at that time. The right and left wings (the left wing commanded by the Plataeans) surrounded the Persians after a seemingly suicidal charge by the centre line.

Although the Greeks were victorious, Callimachus was killed during the retreat of the Persians while he was chasing them to their ships.

Plutarch, in his work: Moralia. Greek and Roman Parallel Stories mentions that Callimachus was pierced with so many spears that, even when he was dead, he continued to be in an upright posture.

Contemporary Athenian custom dictated that the city choose a man held in high regard to deliver an oration over the war dead at the end of public funeral rites. Polemon of Laodicea, a sophist flourishing six centuries after the event, imagined the aftermath of the battle to have occasioned a public dispute between the fathers of Cynaegirus and Callimachus before an Athenian assembly to decide which should give such an oration over the Marathon dead; using this fictional situation to exercise his rhetorical skill, Polemon made declamations for each litigant.

Callimachus was portrayed among the Athenian gods and heroes on the wall-paintings of the Stoa Poikile. The Athenians erected a statue in honour of Callimachus, the "Nike of Callimachus".