Levantine archer auxilia are supporting troops for the heavier legionary infantry, now an important secondary role in Roman warfare.
Specialised archer units for the imperial army can be enrolled in all provinces in which skilled bowyers and a population familiar with the traditions of archery can be found. These are mainly in Asia and the fringes of the steppes.
Archers now have become an integral part of any well composed roman army. Normally they are placed behind a wall of protective heavy infantry in the battle formation. From there they can provide a supporting barrage fire above the infantry’s heads to weaken the enemy and break his charge before the main lines engage.The imperial army’s archers are more heavily armoured than their counterparts, with shirts of lorica squamata or hamata (scale or chain mail), conical iron or bronze helmets and small shields protecting their left arm. They use long ranged recurved composite bows with bone ends and bracers to protect their forearms from the sinew, together with multiple types of arrows: three bladed heads to inflict heavy wounds at unarmoured targets, thin needle like, pyramidal shaped armour piercing heads and flaming arrows, carrying an ignition load in a kind of small metal cage incorporated into the arrowhead. Additionally the archers are armed with a gladius for self defence, but despite this and their armour it should not be expected that they fight well at close quarters for a long time.
Historically, the majority of the specialised archer and horse archer units of the imperial roman army were enrolled in the eastern provinces, especially in Syria, where fine archery skills and the knowledge to make powerful composite bows were backed by traditions that can be dated back well into the Bronze Age. After their formation these troops could be sent to all parts of the empire, where they often begun to recruit locals as replacements. Other than most units of the auxilia, however the specialised archer alae and cohorts still received the bulk of their replacement from their home area. Most of these units were stationed in northern Africa, the lower Danubian Provinces and the east where highly mobile enemies threatened the empire's borders.
During the decades of his rule following the end of the civil war, Augustus reformed the imperial army significantly and created a standing army with 28 legions as its core. In many fields a systematic approach replaced the improvisation of the late republican era. Most important was that the auxilia, with its indispensable cavalry and archer units, became a regular arm of the professional army and its second base.
Trained to the same high standards of the legions they should cooperate with, these excellent soldiers were equipped in the Roman fashion, and well commanded first by proven Centurions, transferred from the legions, and later by a corps of equestrian officers. Their soldiers were mostly recruited from amongst the peregrines, free provincials without roman citizenship, who either volunteered for service or accepted a draft into it. However, the transformation of the auxilia did not happen over night and the irregular contingents of soldiers supplied by allied tribes and vassal states did not disappear all at once. While the large majority of the alae (pure cavalry units where the need for regular forces was more urgent) were reorganized during Augustus reign, the infantry followed much more slowly, lingering in the old fashions until the later years of the 1st century AD.
Most cohorts of the Principate’s auxilia were standard sized cohors quingenaria units, consisting of 480 enlisted soldiers organised in six centuriae. Later in the first century elite approximately double strength cohors millaria and mixed cohors equitata appeared. The equitata units had their own attached cavalry contingent of 120 respectively 240 troopers for the millaria version, so that these units could either operate independently without further assistance or provide a more flexible support for the legions in the case of specialised archer units.
The length of service for all soldiers was finally set to 26 years for fleet soldiers, 25 years for soldiers of the auxilia, 20 years for legionnaires, and 16 years for praetorians. After their discharge they received a cash bonus, the praemia militare, or a small piece of land. The veterans from the auxilia and the fleet were rewarded with Roman citizenship, and a diploma to prove it. Also, medical treatment was improved and all units were now supplied with physicians.