When the Roman armies started being composed partly of Roman citizens and partly of
socii (allies from the rest of the Italian mainland), either Latini or Italici, it became the practice to marshal the Roman troops in the centre of the battle line and the
socii upon the wings. Consular armies of the mid-Republic would consist of two
legions of Roman citizens and two legions of "ala", with the ala supplying thirty turmae of cavalry per legion, whereas the Roman provided only ten turmae. Hence
ala and
alarii denoted the contingent furnished by the
allies, both horse and foot, and the two divisions were distinguished as
dextera ala (right wing) and
sinistra ala (left wing). As late as
Polybius' times, contingents of allies forming the alae were recruited by their own leaders in their homelands, which were expected to levy an equivalent number to the Roman troops; the specifications of those agreements were covered in the
formula togatorum.
Socii were expected to fight in the same manner and equipment as the Roman troops and provide their own basic rations, and were in turn would receive a percentage of any loot gained, although at a lower rate than their Roman equivalents. ==References==