<P> Exploratores ("reconnaissance troops", from explorare = "to scout"): Examples include two numeri exploratorum attested in the 3rd century in Britain: Habitanco and Bremenio (both names of forts). Little is known about such units . </P> <P> Throughout the Principate period, there is evidence of ethnic units of barbari outside the normal auxilia organisation fighting alongside Roman troops . To an extent, these units were simply a continuation of the old client - king levies of the late Republic: ad hoc bodies of troops supplied by Rome's puppet petty - kings on the imperial borders to assist the Romans in particular campaigns . Some units, however, remained in Roman service for substantial periods after the campaign for which they were raised, keeping their own native leadership, attire and equipment and structure . These units were variously called by the Romans socii ("allies"), symmachiarii (from symmachoi, Greek for "allies") or foederati ("treaty troops" from foedus, "treaty"). One estimate puts the number of foederati in the time of Trajan at c. 11,000, divided into c. 40 numeri (units) of c. 300 men each . The purpose of employing foederati units was to use their specialist fighting skills . Many of these would have been troops of Numidian cavalry (see light cavalry above). </P> <P> The foederati make their first official appearance on Trajan's Column, where they are portrayed in a standardised manner, with long hair and beards, barefoot, stripped to the waist, wearing long trousers held up by wide belts and wielding clubs . In reality several different tribes supported the Romans in the Dacian wars . Their attire and weapons would have varied widely . The Column stereotypes them with the appearance of a single tribe, probably the most outlandish - looking, to differentiate them clearly from the regular auxilia . Judging by the frequency of their appearance in the Column's battle scenes, the foederati were important contributors to the Roman operations in Dacia . Another example of foederati are the 5,500 captured Sarmatian cavalrymen sent by Emperor Marcus Aurelius (r . 161--180) to garrison a fort on Hadrian's Wall after their defeat in the Marcomannic Wars . </P> <P> As had been the case during the Republic, the legions of the Principate era recruited Roman citizens exclusively . In the 1st and 2nd centuries, these represented a minority of the empire's inhabitants (about 10--20%). From the time of Augustus, legionary recruitment was largely voluntary . Republican - style conscription of citizens was only resorted to during emergencies which demanded exceptionally heavy recruitment, such as the Illyrian revolt (AD 6 - 9). </P>

Could you get married if you were in the roman army