You still have it wrong friend.
Marian reform army is the army Caesar used. Marian reforms happened only a few decades before Caesar started his Gallic conquests. And technically, the "Marian Reform" army is what was used up through most of the reign of Augustus. He was the one who created the standing army of the Romans that many know and love, standardiing many of the ad hoc practices of the previous 80 years since the Marian Reform. About that tme is when the segmentata became into use, very early 1st century AD. Continued to being used until the 3rd century AD. I would say the peak of use was in the reign of Trajan and his Dacian Wars, around AD 105. Hamata was used too through the whole time period.