It is important to view the Roman army as a constantly evolving institution. Armor, clothing, formations, and unit organization altered over time, as the army encountered and adapted to changing situations.

The stark equipmental differences seen in Roman iconography such as Trajan’s Column is an artistic convention. This was a stylistic choice, designed to clearly differentiate the two troop types to a populace which likely had never seen a provincial soldier. Although different to an extent (mail appears to have been more popular, though regular finds of pieces of segmented armor in auxiliary forts indicate it’s use), auxiliary equipment tended to converge with, and influence, legionary equipment over time. Thus, by the reign of Caracalla, the tactical difference between legionary and auxiliary infantry (which had never really been significant) was relatively minute.

Throughout the period of the Principate, Roman citizenship spread to many differing individuals and communities, either by imperial grant or auxiliary service. This extension of citizenship, coupled with the stationing of the army along the frontier, rapidly accelerated the army's “provincialization”. By the second century A.D., Italians ceased to be significantly represented in the ranks. Instead, the legions were comprised of provincials, recruited locally and fostered by the army with a unique definition of "Roman-ness". Auxiliary soldiers, always provincials, had a similar experience, with the added benefit of citizenship at the completion of their service. While citizenship was a key prerequisite to legionary service, in times of crisis, the army likely didn’t look to heavily at a recruit’s background.

Although the Edict of Caracalla removed a strong incentive for auxiliary service, the army still offered many tangible benefits. Most recruits were came from poor, rural backgrounds, drawn heavily from more peripheral, less wealthy areas such as Illyria and Pannonia. For a young man used to a subsistence existence, military service offered decent pay (doubtless for many their first experience with “disposable income”), food security, and excellent medical care. There were also less tangible benefits, such as the prospect of adventure and social advancement, especially during the third century, when several common soldiers found themselves wearing the purple. Even without a grant of citizenship, military service remained an attractive occupation.

The Edict of Caracalla, while highly significant in Roman legal history, does not appear to have had a major effect on the composition of the army. If anything, it accelerated the amalgamation of auxiliary and legionary equipment and organization. Units continued to recruit local men largely of poor provincial extraction, drawn to military service by it’s tangible benefits.