[2] Some theories propose the idea that Nero began to recruit marines from the Misenum navy, and Galba likely was responsible for the last stages of the organization, when sacrifices were made, and the legion received its aquila standard.

The city of Moguntiacum (Mainz) is the legion's first known base camp, shared with Legio XIV Gemina, where they attended mainly building activities.

Following the murder of Domitian in 96, the Adiutrix, along with the Danubian army, played an important role in Roman politics, forcing Nerva to adopt Trajan as his successor.

[5] Between 101 and 106, under the new emperor's command, I Adiutrix, along with IV Flavia Felix and XIII Gemina, conquered Dacia and occupied the newly formed province.

In the next decades, the main base was again Pannonia, but they played a part in several Parthian wars, namely the campaigns of 195 and 197–198 of Septimius Severus, 215–217 led by Caracalla and 244 by Gordian III.