Spaul John. ALA²: The Auxiliary Cavalry Units of the Pre-Diocletianic Imperial Roman Army

Nectoreca Press, 1994. — 327 p.An Ala was the term used during the middle of the Roman Republic (338-88 BC) to denote a military formation composed of conscripts from the socii, Rome's Italian military allies. A normal consular army during the period consisted of two legions, composed of only Roman citizens, and two allied alae. The alae were somewhat larger than normal legions (ca. 5,400 v. ca. 4,500 men). From the time of the first Roman emperor, Augustus (ruled 30 BC - AD 14), the term ala was used in the professional imperial army to denote a much smaller (ca. 500), purely cavalry unit of the non-citizen auxilia corps: see ala (Roman cavalry unit). Armies of the middle 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).