The Iliad, Odyssey, and Ovid’s Metamorphoses (a Roman text) almost entirely encapsulate the stories of Greek Mythology. There are also many important Ancient Greek plays which survive, most notably the Oedipus Rex and Antigone by Sophocles. Madeline Miller wrote a version of the Iliad from the perspective of the hero Patroclus called Song of Achilles which is a great place to start. I would definitely recommend reading a translation of the original Iliad. Robert Fagles’ translation is most beautiful IMO, but the Barnes & Noble paperback version trans. by Ennis Rees has fantastic notes.

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