VOLONES is synonymous with Voluntarii (from volo), and might hence be applied to all those who volunteered to serve in the Roman armies without there being any obligation to do so. But it was applied more especially to slaves, when in times of need they offered or were allowed to fight in the Roman armies. Thus when during the second Punic war after the battle of Cannae there was not a sufficient number of freedmen to complete the army, about 8000 young and able-bodied slaves offered to serve. Their proposal was accepted; they received armour at the public expense, and as they distinguished themselves they were honoured with the franchise (Liv. xxii.57, xxiii.35; Macrob. Sat. i.11; Festus, s.v. Volones). In after times the name volones was retained whenever slaves chose or were allowed to take up arms in defence of their masters, which they were the more willing to do, as they were generally rewarded with the franchise (Liv. xxiv.11, 14, &c., xxvii.38, xxviii.46; J. Capitolin. M. Antonin. Philos. 21).

William Smith, A Dictionary of Greek and Roman Antiquities (London: John Murray, 1875), 1217.