Entremont is in the middle of what we now call Provence. (in fact that name Provence comes from the name the Romans gave that area)
It is just east of Languedoc.
The timescale for the Entrement hillfort is 350BC-123BC.
At this time this region was one of most important in entire area economically.
Rome was growing, and is closeby.
Romans began interventions in "Spain" . Along the coast though Provence was an extremely importan trade route for the Romans.
Entrement is on this trade route, via Languedoc on the coast.
Trade becomes more important; and so Entremont grows with this trade.
The Celtic group that live in this area are the Ligurians~most populous and powerful of Celtic Confederacy.
For a long time they were happy to accomodate this trade.

But Rome started the process of annexation of Ligurian territory~they attacked and raised down Entremont in 123BC; and created the Province.