Though traces of Neolithic settlements can be found in the region, the earliest modern settlements on the site were Celtic Tharsatica (modern Trsat, now part of Rijeka) on the hill, and the tribe of mariners, the Liburni, in the natural harbour below. The city long retained its dual character. Rijeka was first mentioned in the 1st century AD by Pliny the Elder as Tarsatica in his "Natural History" (iii.140).. Rijeka (Tarsatica) is again mentioned around AD 150 by the Greek geographer and astronomer Ptolemy in his Geography when describing the "Location of Illyria or Liburnia, and of Dalmatia" (Fifth Map of Europe).