There were the "Auxilium" or the Auxiliary Cohorts. They could be Gallic, some Germanic,
Syrian, Nabatean, Numidian. You have an assortment of nations that were recruited by the Romans. Titus, when besieging Jerusalem had a mixture of Italic as well as Syrian conscripts
that formed the most famous Legion the "X Fretensis" (The Tenth Legion). You also had the famous Slingers from Thrace, Hamian Archers from the Osrohene (Southern Armenia). Titus, and for that matter, Rome as a whole had a multitude of differnet nationalities in the
ranks of the Roman Legions. Hope this helps. Read "WARRIORS OF ROME" by Michael Simkins.