Which Greek Stoic philosopher mentioned two of the four subgroups of the Helvetians that failed in their migration attempt to Gaul?
Helvetii: The Helvetii (Latin: "Helvētiī" ] ) 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. Helvetii:  According to Julius Caesar, the Helvetians were divided into four subgroups or "pagi." Posidonius: Posidonius (Greek: Ποσειδώνιος, "Poseidonios", meaning "of Poseidon") "of Apameia" (ὁ Ἀπαμεύς) or "of Rhodes" (ὁ Ῥόδιος) (c. 135 BCE – c. 51 BCE), was a Greek Stoic philosopher, politician, astronomer, geographer, historian and teacher native to Apamea, Syria.
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