The Helvetii were a Gallic tribe or tribal confederation occupying most of the Swiss plateau at the time of their contact with the Roman Republic in the 1st century BC. According to Julius Caesar, the Helvetians were divided into four subgroups or pagi. Of these Caesar only names the Verbigeni and the Tigurini, while Posidonius mentions the Tigurini and the Tougeni . They feature prominently in the Commentaries on the Gallic War, with their failed migration attempt to southwestern Gaul (58 BC) serving as a catalyst for Caesar's conquest of Gaul.