Plato's Republic was originally written around 375 B.C.E. The Republic is a work of philosophy, more specifically a Socratic dialogue. Indeed, the story is a fictional conversation between Socrates and many interlocutors, and philosophical arguments are advanced and refuted by the characters over the course of their conversation. While the specifics of The Republic are widely considered by scholars to be fictionalized, Plato was in fact a student of Socrates and is one of the best and only surviving sources on Socrates's teachings.
The Republic is one of the most famous and influential works of philosophy ever written. Belonging to the classical literary tradition alongside other surviving foundational Greek and Roman texts, The Republic and other books by Plato were foundational to Platonism and Neoplatonism. They were equally foundational but contrasting in some ways to Aristotelianism, as Aristotle was a student of Plato.
The Republic belongs to the same literary and philosophical traditions as Plato's other socratic dialogues, like Phaedrus and Crito, which similarly bridge the gap between works of fiction and philosophy. Although The Republic is a work of philosophy, as a fictional conversation it is almost a kind of historical fiction. Regardless, Plato's Republic uses figurative language extensively to support, indict, and/or otherwise further the arguments and counter-arguments made throughout the story.