Lewis & Short

Narnĭa, ae. f.,

  1. I. an Umbrian city on the Nar, now Narni, Liv. 10, 10; 27, 9; 29, 15; Tac. A. 3, 9.
    Hence,
  2. II. Narnĭensis, e, adj., of or belonging to Narnia, Narnian: ager, Plin. 31, 4, 28, § 51: equites, Liv. 27, 50.
    As subst.: (sc. ager), Plin. Ep. 1, 4, 1.
    In plur. subst.: Narnĭenses, ĭum, m., the inhabitants of Narnia, the Narnians, Plin. 3, 14, 19, § 113.