Appian(us) (c.AD 95 – c. 165) was born in Alexandria but went to Rome in c.120 to practice law. We are not entirely sure about what sources he used for his histories.
The following is an adaptation of Appian. The Foreign Wars, trans. Horace White. New York: MacMillan Company, 1899.
§ 1.2. They say that the country [Illyria] received its name from Illyrius, the son of Polyphemus; for the Cyclops Polyphemus and his wife, Galatea, had three sons, Celtus, Illyrius, and Galas, all of whom migrated from Sicily; and the nations called Celts, Illyrians, and Galatians took their origin from them. Among the many myths prevailing among many peoples this seems to me the most plausible. Illyrius had six sons, Encheleus, Autarieus, Dardanus, Mædus, Taulas, and Perrhæbus, also daughters, Partho, Daortho, Dassaro, and others, from whom sprang the Taulantii, the Perrhæbi, the Enchelees, the Autarienses, the Dardani, the Partheni, the Dassaretii, and the Darsii. Autarieus had a son Pannonius, or Pæon, and the latter had sons, Scordiscus and Triballus, from whom nations bearing similar names were derived.
§ 1.4. The Autarienses were overtaken with destruction by the vengeance of Apollo. Having joined Molostimus and the Celtic people called Cimbri in an expedition against the temple of Delphi, the greater part of them were destroyed by storm, hurricane, and lightning just before the sacrilege was committed. Upon those who returned home there came a countless number of frogs, which filled the streams and polluted the water. The noxious vapors rising from the ground caused a plague among the Illyrians which was especially fatal to the Autarienses. At last they fled from their homes, and as the plague still clung to them (and for fear of it nobody would receive them), they came, after a journey of twenty-three days, to a marshy and uninhabited district of the Getæ, where they settled near the Bastarnæ. The god visited the Celts with an earthquake and overthrew their cities, and did not abate the calamity until these also fled from their abodes and made an incursion into Illyria among their fellow-culprits, who had been weakened by the plague. While robbing the Illyrians they caught the plague and again took to flight and plundered their way to the Pyrenees. When they were returning to the east the Romans, mindful of their former encounters with the Celts, and fearful lest they should cross the Alps and invade Italy, sent against them both consuls, who were annihilated with the whole army. This calamity to the Romans brought great dread of the Celts upon all Italy until Gaius Marius, who had lately triumphed over the Numidians and Mauritanians, was chosen commander and defeated the Cimbri repeatedly with great slaughter, as I have related in my Celtic history. Being reduced to extreme weakness, and for that reason excluded from every land, they returned home, inflicting and suffering many injuries on the way.