Caesar starts off with 4 legions but the first thing he does is raise 2 legions. Then in the second year he raises 2 further legions.
Caesar says nothing about where the money came to pay for this.
None of the modern accounts of the Gallic wars even pose the question let alone answer it,
The first 2 legions, I guess, must have been from the resources of his 3 provinces (well 2 and a ...