Calchas (/ˈkælkəs/; Ancient Greek: Κάλχας, Kalkhas) is an Argive mantis, or "seer" in Greek mythology. Calchas appears in the opening scenes of the Iliad, which is believed to have been based on a war conducted by the Achaeans against the powerful city of Troy in the Late Bronze Age.
A seer in the service of the Greek forces, Calchas is portrayed as a skilled augur, Greek oinópolos ('bird-savant'): "as an augur, Calchas had no rival in the camp." He had received knowledge of the past, present, and future from the god, Apollo. He had other mantic skills as well: interpreting the entrails of the enemy during the tide of battle. His mantosune, as it is called in the Iliad, is the hereditary occupation of his family, which accounts for the most credible etymology of his name: “the dark one” in the sense of “ponderer,” based on the resemblance of pondering to melancholy, or being “blue.” Calchas has a long literary history after Homer. In the legendary time of the Iliad, seers and divination are already long-standing.