The term derives from the name of one Ibero-Celtic tribe, the Lusitani, that lived in the north-western part of the Iberian Peninsula prior to the Roman conquest; the lands they inhabited were known as Lusitania. The Lusitani were mentioned for the first time, by Livy in the 1st century BCE, as Carthaginian mercenaries who were incorporated in the army of Hannibal when he fought the Romans. Pliny the Elder states in "Naturalis Historia" (77–79 CE) that the Lusitanians were Celtiberians in particular, and ancestral to the Celtici of Baetica (now western Andalusia, Spain).