Lewis & Short

2. Pŏpŭlōnĭa, ae, f., also Pŏpŭlō-nĭum, ĭi, n., and Pŏpŭlōnĭi, ōrum, m.,

  1. I. a town on the coast of Etruria, now the ruins of Poplonia, near Piombino.
    Form Populonia, Verg. A. 10, 172; Mel. 2, 4, 9: Populonium, Plin. 3, 5, 8, § 50: Populonii, Liv. 30, 39, 2.
    Hence,
  2. II. Pŏpŭlōnĭen-ses, ĭum, m., the inhabitants of Populonia, the Populonians, Liv. 28, 45.