In Homer’s Iliad, Apollo sends a plague against the Greek army at Troy. The god acts after Agamemnon refuses to return Chryseis, the daughter of Apollo’s priest Chryses. Chryses prays for vengeance, and Apollo answers by shooting arrows into the Greek camp for nine days.
The plague ends only after Agamemnon gives Chryseis back and the Greeks perform the proper sacrifice. Agamemnon then takes Briseis from Achilles as compensation, provoking the quarrel that drives the central action of the Iliad.
Apollo supports Troy throughout much of the poem and repeatedly helps its defenders. His role is not the same as Ares’ role: Ares is the god associated with violent warfare, while Apollo appears here as an archer, healer, and divine agent of disease. The opening crisis therefore links religious offense directly to the human conflict between Agamemnon and Achilles.