Auxilia palatina is the technical name in Roman history for infantry units first raised by Constantine the Great as part of the new field army he created in about 325 AD. Some of the senior and probably oldest of these units had special names such as Cornuti or Brachiati; others were named after the tribes from which they were recruited (many of these in eastern Gaul, or among the German barbarians). These units all became palatine units when a distinction was drawn between palatini and the remainder of the comitatenses around 365. There is no direct evidence for the strength of an auxilium, but A H M Jones (History of the Later Roman Empire, Blackwell, Oxford, 1964 p 682) estimates that it may have been 600 or 700. Some auxilia are attested as limitanei, especially on the Danube. It is not clear whether these were regarded as a different category of unit. Constantine. ...
Each Legion had a same size or near same size Auxilia (auxiliary), which contained specialist units, engineers and pioneers, artillerymen and siege craftsmen, service and support units plus units made up of non-citizens (who were granted Roman citizenship upon discharge) and undesirables.
There is no evidence to suggest that Legions changed in form before the Tetrarchy, although there is evidence that they were smaller than the paper strengths usually quoted.
The final form of the Legion originated with the elite Legiones palatinae created by Diocletian and the Tetrarchs.