Both these terms, although their history is widely different, originate in the military terminology of the Republic. The term _cohors_ had been originally applied to the infantry contingents of the Italian _socii_, which were not united in legions after the model of the levies of _cives Romani_, and it was naturally retained after the disappearance of the _socii_ to describe the similar tactical units of provincial auxilia. The term _ala_ originated as a metaphorical description of the two divisions into which the contingents of _socii_ were formed, which were stationed in the normal republican order of battle on either flank of the legions. After the disappearance of the _socii_ the term was applied in a more restricted sense to the two flanking divisions in which the average Roman general massed all his available cavalry. This use of the word continued down to the last days of the Republic. When, for instance, the author of the _De bello Africo_ writes, ‘Caesar _alteram_ alam mittit qui satagentibus celeriter occurreret,’[34] or Cicero says of his son in the _De Officiis_, ‘Quo tamen in bello cum te Pompeius _alteri_ alae praefecisset, magnam laudem et a summo viro, et ab exercitu consequebare equitando, iaculando …’[35] the word is clearly being used in this sense, and does not refer to a regiment of any fixed size. In fact the cavalry of the _socii_ never seem to have been organized in larger units than _turmae_, and the auxiliary levies naturally adopted the same formation. It has already been noticed that some of the Spanish auxiliaries who served in the Social War are officially described as belonging to a _turma Salluitana_. Occasional phrases in Livy, such as the statement that the Aetolian cavalry contingent, in the campaign of 171 B.C., was _alae unius instar_, do not seem to prove anything more than that the historian used the technical terms of his own age to make his narrative clearer.[36] This usage, however, shows that Livy was familiar with the restricted meaning of the word—that is to say, the ala must have been a recognized institution in the reign of Augustus, and we may add that Velleius states that fourteen alae were employed in the Pannonian campaigns of 6-9 in which he himself had served. It is improbable, however, that the ala was a creation of Augustus, although he may have determined its exact size and organization. In Caesar’s account of his Gallic campaigns we find frequent mention of contingents of tribal cavalry serving as independent units under officers bearing the title of _praefecti equitum_,[37] and these units must have been much larger than _turmae_. The organization of these regiments, originally of a purely temporary kind, must have been placed on a more permanent basis when many of them were taken out of their own country to serve in the Civil Wars, and it would have been natural that a new term should be used to describe them.[38]