About Celtic Texts (600-100 BCE)
Celtic texts are found throughout Switzerland and the Po Valley as shown by the markers on this map. Most are short inscriptions on pottery with the Bronze Liver from Piacenza being a notable exception. Because of its long inscription the Piacenza liver was incorrectly classified as Etruscan.
Celtic culture is a more general term for the Hallstatt and Le Tene cultures who acquired their wealth from salt out of Salzburg, Austria and the trade along the Danube/Rhine axis. People from Malta at least played a part in this culture's origin.
Map from website: The Cisalpine Celtic Languages which is an ongoing European research project edited by David Stifter, Martin Braun, Corinna Salomon, Michela Vignoli et al. It is online at: https://lexlep.univie.ac.at/wiki/The_Cisalpine_Celtic_Languages#Definition_of_%22Ligurian%22
Central Celtic Halstatt and La Tene Cultures (1300- 500 BCE)
Hallstatt (yellow) and La Tène (green) cultures. The Proto-Celtic Hallstatt culture was located at the European trade center incorporating the salt mines near Salzburg and the portage between the Danube and Rhine rivers.
Information from Atlas of the Celtic World, by John Haywood; London Thames & Hudson Ltd., 2001, pp. 30-37.
By Dbachmann via Wikimedia Commons at: https://commons.wikimedia.org/wiki/File:Hallstatt_LaTene.png
Neolithic Era - Maltese Female Gene Types in Red
Late Bronze Age Era - Maltese Female Gene Types Show Survival in Hallstatt Culture
Organized salt mining began around Hallstatt (Salzkammergut region) in the Bronze Age starting around 1600 BCE. Before then water was boiled from salt springs to get the salt. This Central Celtic culture is different from the Eastern Celtic culture of pre-Roman Britain although an early connection does seem to exist.