The name Narnia was derived from Narni, an Italian city.
Lewis encountered the name in an atlas and used it for the fictional land at the center of his fantasy chronicles. Narni is a historic hill town in the Italian region of Umbria, south of Perugia. Its ancient Latin name was Narnia, which supplied the form Lewis adopted.
The connection is a name source rather than a claim that the fictional kingdom reproduces the Italian town. Narnia contains its own geography, peoples, chronology, and mythology, including Cair Paravel, Lantern Waste, and the eastern sea. Lewis’s use of an existing place-name illustrates how real geography can provide a memorable starting point for invented worlds.
Readers sometimes assume that Narnia’s name was created entirely from scratch or that it directly refers to a Celtic word. Lewis’s own explanation points instead to the atlas discovery of the Italian place-name. The similarity is especially clear because Narni’s ancient Latin form is spelled Narnia.