Cohorts ingenuorum

[The Alexandrian]

'cohortes ingenuorum' and 'voluntarium civium Romanorum'

If I understand correctly, these were auxiliary cohorts raised by Augustus that in his will he had turned into units with citizen, "legionary" status.

Can anyone provide me with any information or sources on these units? Where were they raised, how were they armed, and most of all, what happened to them on the death of Augustus? Were they merged with legions? Or did they continue to operate as smaller auxiliary cohorts whilst maintaining their new citizen status? When are they lasted attested in epigraphic evidence?

[Vincula]

I found this: http://www.romanarmytalk.com/rat/viewtopic.php?f=17&t=26986