The Helvetii (in Latin) were the Celtic inhabitants of modern Switzerland.

They were described by Julius Caesar in his De Bello Gallico.

Under pressure from Germanic tribes in their home territory, they were planning to migrate into Gaul with their entire tribe under the command of Orgetorix. Caesar was called upon by the Gauls of the province of Gallia Narbonensis, which had already been conquered, to defend them from the invading Helvetii.

Caesar, at the time, commanded six legions comprised of nearly 290,000 men. The Helvetii, according to Caesar's writings, had 370,000 people (including children and women), but only 110,000 men-at-arms. Caesar hastily recruited two more fresh legions in preparation.

By the time the tribe began its march, Orgetorix had died. Before leaving, the Helvetii burned their villages and destroyed what foodstuff and other commodities they could not take with them so that they could not turn back.

Lured to a disadvantageous position with the Romans taking the high ground near the Aedui capital of Bibracte, the Helvetii were attacked by the superior Roman forces, who managed to kill nearly 60 percent of the tribe and capture another 20 percent as slaves. The remainder of the Helvetii were driven back into their old lands, Helvetia.

In 52 BC, 10,000 Helvetii joined Vercingetorix's forces in his attempt to liberate Gaul.